It's mildly amusing that AO3 is considered more palatable than booru websites. Both AO3 and many of the boorus have content that would be hard for most folks to stomach. I guess AO3 has the advantage of being mostly text, (which seems to be generally less visceral to people,) but it is also nearly completely uncensored, since that's kind of the point of it.
Yes, overall I wouldn't describe either of them as particularly palatable to a general audience, haha. Your hunch is the same as mine -- text has much less potential for instant shock. On AO3 you have to, sort of, go out of your way (by reading, or searching for specific tags, etc.) to hit the unsavory stuff.
Even if you did find the unsavoury stuff on Ao3 it might take a while to get to it in the story whereas in an image you could be blasted with the sin of more than a thousand words all at once
