Your comments
Downvoting you wasn't an insult, I didn't like the alternative idea so I downvoted it. [Likewise the following downvote for the comment I'm replying to isn't out of spite but due to the passive agressive insult you included calling anyone who uses the filtering system a baby.]
Leaving out the option for multiple tags for the moment [something that could work in addition to this idea, it doesn't have to be separate from it.]
The method you are promoting is cumbersome and would be a lot more work for the user.
With my idea you would enter the tag [or multiple if that also got implemented] then you would be able to select 1, 2 or all 3 ratings to be filtered out.
With your idea you'd save time filtering all three as you wouldn't have to select anything [the exact system we have now,] but you'd double the number of filter tags you'd have to manually add to filter two of the ratings, which simply doesn't make sense when tickboxes and such would do it so much easier and faster and doesn't risk user error in spelling explicit, mature or clean.
My idea actually isn't just about the cub issue though.
I actually mean it as displayed [though that would simplify the cub filter example XD.]
I really do think it would be good to be able to filter things based on rating. I'm gay and while I don't hate straight porn I'm not interested in it but blocking it outright when clean work might be really nice would be a waste.
Also, as silly as the watersports example is, I'm sure there are some terms that mean one thing in porn but another outside of porn that people would want to block without blocking from general.
I don't mean that there should be a pre-made table, I mean that when you create a filter it creates a table [or whatever] with the ability to click which of the ratings it filters.
So you would just add the tag straight, click add, then click the options next to it [or those could be there at the typing stage.]
The table I included was just to illustrate what I was trying to say as I know I often fail to convey my ideas properly.
I think that's much better than having to add each tag like your example and should be relatively easy to code [I think.]
While this could be a good solution, and absolutely SHOULD happen if it's not banned, it doesn't even slightly address the issue of legal risk to users in certain parts of the world.
If it's posted it's a possible risk by association, if it's posted and not tagged even more risky.
While I do not beleive there have been any cases of people being prosecuted for cub porn [unless they had actual child porn like Gembeck,] there HAVE been cases of people being prosecuted for child porn manga.
https://uk.news.yahoo.com/manga-anime-fans-warned-british-man-convicted-possessing-113808103.html
We can argue all we want that there is a difference between drawing of children and drawing of animal children but we don't have a say in it, it's down to the courts and I'd rather stay far away from that risk.
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Also, my idea futureproofs itself.
If they add more ratings beyond just general, mature and explicit that just requires them to rename the tickboxes and add extras for the users to select.
Your idea would require them to modify all filters that use the current terms and for users to edit each one to add any new terms to them.
It also wouldn't differentiate between the rating mature, and the tag mature [for character age.]