Certain gTLDs have been borderline scams. The most infamous one might be .sucks, an extortion scheme charging an annual protection fee of $$$, complete with the pre-registration process when you could buy <yourtrademark>.sucks for $$$$ before it’s snatched up by your enemies.

They also screwed up some old URL/email parsers/sniffers hardcoding TLDs. Largely the fault of bad assumptions to begin with.

Other than the above, I don’t see much of a problem. Whatever problems people like to point out about gLTDs already existed with numerous sketchy ccTLDs, like .io. Guess what, the latest hotness .ai is also one of those.