No AI needed. Spam on the internet is a great example of the amount of unreasonable people on the internet. And for this I'll define unreasonable as "committing an action they would not want committed back at them".
AI here is the final nail in the coffin that many sysadmins have been dealing with for decades. And that is that unreasonable actors are a type of asymmetric warfare on the internet, specifically the global internet, because with some of these actors you have zero recourse. AI moved this from moderately drowning in crap to being crushed under an ocean of it.
Going to be interesting to see how human systems deal with this.
The ability to create spam instantly, fitted perfectly to any situation, and doing that 24/7, everywhere, is very different from before. Before, spam was annoying but generally different enough to tell apart. It was also (in general) never too much as to make an entire platform useless.
With AI, the entire internet IS spam. No matter what you google or look at, there's a very high chance it's AI spam. The internet is super duper extra dead.
At least a bunch of lawyers already got hit when their court filings cited hallucinated cases. If this trend continues, I'll not be surprised when some end up disbarred.
AI also generates spam though, so this is a much bigger problem than merely "unreasonable" people alone.
Now, with that said I don't think we're very far from automated agents causing problems all on their own.