I think the parent comment was implying that people will stop using services that end in ".io" or ".co" or, really, anything but ".com" because of the large number of shady websites on the off-brand TLDs.

There are an order of magnitude larger number of untrusted domains on '.com' than any of these new ones.

But many trusted ones are, and most importantly most of the ones a user interacts with are legit.

If a significant portion of the domains a user visits on a new TLD are shady, they may just write it off.