It sucks to be on both sides of this issue, but having easily-accessible, clear and concise lists is just the best solution/compromise for both. Having nothing spoilered sucks on one end, and having long-ass lists with way more information than necessary that are cumbersome to browse sucks for people with memory issues. I encourage discords to have a list of what needs to be spoilered, and to keep it as minimal in format as possible.
I think my personal best way to do it would be to have a channel right below the rules channel called like "spoilered fr content" and have it have a clear, concise list. Something like, for example:
"Please spoiler the following content on dragons when posted in this discord: - Shadow/Plague Primal - Multigaze - Jaguar/Rosette - Gembond"
(Idk what other new genes/other stuff may be triggering to people, I was just listing the three things I've seen mentioned most as well as something vaguely similar to make the list slightly longer in size.)
Something clear and concise like that is a fair compromise where it's very accessible to check if you have memory problems (no one is saying anyone has to remember anything, and as long as the list is clear and concise, it shouldn't be an issue to check your dragon you want to post), but also accommodates for the most common triggers.
Ultimately, it comes down to communicating one's needs. If a person has memory problems and the list format of the discords they're in is written weirdly, hard to find, or has way more information than needed which makes it a longer read and they've forgotten the beginning by the time they get to the end (trust me, been there, done that...), then they should poke at a member of the mod team and ask them if it can be formatted differently to make it easier on them. Chances are, as long as they're polite and considerate about it and express what they need, the mods will be willing to work with them on finding a middle ground that also works for the memory issues.
If they're not willing to consult a list *at all* ever even when formatted clearly and cleanly, yeah, no, that's just being insensitive and selfish. (I do genuinely try to take most users who claim a disability at face value and work with them to try and find solutions, but sometimes you do run into someone who's very clearly just trying to not bother with common courtesy and play their way and only their way with getting exceptions baked into rules for their royal ass.)
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As a side note to you on your personal theory -- I'm assuming you have no problems with content on the site, but for me personally, shadow/plague primal make me physically ill to see. Like literally physically ill. I'm not going into the details on this post directly to avoid making other people uncomfortable, but if you really need to know, you can check https://pastebin.com/HUAkggsn which explains the symptoms I personally experience. Something doesn't have to be related to RL traumatic events to still provoke a visceral, physical reaction in someone, and I wouldn't considered it "unearned moral weight" to want to not be made ill just because I'm in a community discord.
Also, as a note to your point 3 -- I haven't gone to Dragon Share since the release of primal eyes. I don't really actively play much anymore in general, but when I did, it was easy enough to avoid the primal eyes because the main things I did were economy related. I'd see dragons in the coli when buying fodder or when raffle attending, but if I knew I was going to be doing an activity like that where I would see random dragons that may have Primal, I'd just set the site to 70% zoom and between that and the smaller previews in the AH and PAs, it was extremely easy to just miss the primal eyes and not see them if they ever existed. (I did also have a note on my attendant cell to "pls don't send me shadow/plague primal," but I took my own steps to mitigate it on my end as well.) I don't know whether that would help with the trypophobia genes that are on much larger sections of dragons, but at least for something like primal eyes, it was very doable. I did unfortunately have to leave a few community discord servers that weren't willing to accommodate on the primal eyes, but ultimately, most of them ended up understanding and being willing to work with people who communicated their needs.
Also, generally, it does make sense to request spoilering in a discord server because generally, a user cannot prevent discord from loading images themselves (adblock) or change the size at which the image is displayed (zoom level on a browser). The most common workarounds that work on the site itself on the user's end just don't work in community discords, so the only option left really as a bandaid fix is to just have the "spoiler it if you're gonna post it" option.
Re: Censoring genes/eye types on Discord
It sucks to be on both sides of this issue, but having easily-accessible, clear and concise lists is just the best solution/compromise for both. Having nothing spoilered sucks on one end, and having long-ass lists with way more information than necessary that are cumbersome to browse sucks for people with memory issues. I encourage discords to have a list of what needs to be spoilered, and to keep it as minimal in format as possible.
I think my personal best way to do it would be to have a channel right below the rules channel called like "spoilered fr content" and have it have a clear, concise list. Something like, for example:
"Please spoiler the following content on dragons when posted in this discord:
- Shadow/Plague Primal
- Multigaze
- Jaguar/Rosette
- Gembond"
(Idk what other new genes/other stuff may be triggering to people, I was just listing the three things I've seen mentioned most as well as something vaguely similar to make the list slightly longer in size.)
Something clear and concise like that is a fair compromise where it's very accessible to check if you have memory problems (no one is saying anyone has to remember anything, and as long as the list is clear and concise, it shouldn't be an issue to check your dragon you want to post), but also accommodates for the most common triggers.
Ultimately, it comes down to communicating one's needs. If a person has memory problems and the list format of the discords they're in is written weirdly, hard to find, or has way more information than needed which makes it a longer read and they've forgotten the beginning by the time they get to the end (trust me, been there, done that...), then they should poke at a member of the mod team and ask them if it can be formatted differently to make it easier on them. Chances are, as long as they're polite and considerate about it and express what they need, the mods will be willing to work with them on finding a middle ground that also works for the memory issues.
If they're not willing to consult a list *at all* ever even when formatted clearly and cleanly, yeah, no, that's just being insensitive and selfish. (I do genuinely try to take most users who claim a disability at face value and work with them to try and find solutions, but sometimes you do run into someone who's very clearly just trying to not bother with common courtesy and play their way and only their way with getting exceptions baked into rules for their royal ass.)
------
As a side note to you on your personal theory -- I'm assuming you have no problems with content on the site, but for me personally, shadow/plague primal make me physically ill to see. Like literally physically ill. I'm not going into the details on this post directly to avoid making other people uncomfortable, but if you really need to know, you can check https://pastebin.com/HUAkggsn which explains the symptoms I personally experience. Something doesn't have to be related to RL traumatic events to still provoke a visceral, physical reaction in someone, and I wouldn't considered it "unearned moral weight" to want to not be made ill just because I'm in a community discord.
Also, as a note to your point 3 -- I haven't gone to Dragon Share since the release of primal eyes. I don't really actively play much anymore in general, but when I did, it was easy enough to avoid the primal eyes because the main things I did were economy related. I'd see dragons in the coli when buying fodder or when raffle attending, but if I knew I was going to be doing an activity like that where I would see random dragons that may have Primal, I'd just set the site to 70% zoom and between that and the smaller previews in the AH and PAs, it was extremely easy to just miss the primal eyes and not see them if they ever existed. (I did also have a note on my attendant cell to "pls don't send me shadow/plague primal," but I took my own steps to mitigate it on my end as well.) I don't know whether that would help with the trypophobia genes that are on much larger sections of dragons, but at least for something like primal eyes, it was very doable. I did unfortunately have to leave a few community discord servers that weren't willing to accommodate on the primal eyes, but ultimately, most of them ended up understanding and being willing to work with people who communicated their needs.
Also, generally, it does make sense to request spoilering in a discord server because generally, a user cannot prevent discord from loading images themselves (adblock) or change the size at which the image is displayed (zoom level on a browser). The most common workarounds that work on the site itself on the user's end just don't work in community discords, so the only option left really as a bandaid fix is to just have the "spoiler it if you're gonna post it" option.