[yorwba]

Alice profits by not having her post be drowned out by a flood of automated spam. 4chan's users benefit by not having to look for interesting content among a flood of automated spam. 4chan's operators benefit by not having to moderate a flood of automated spam.

If captchas weren't useful to 4chan, they wouldn't make use of it. When you see a system that's obviously not beneficial to anyone, it's useful to take a step back and think about the incentives that keep things as they are. Because if it's so obviously wrong, why hasn't it been changed yet?

I'm not sure how a content-addressed web would handle these problems, but there'll need to be some hoops to jump through before a significant number of other people become willing to look at your content.