The claim is that it is full of tankies. In fact what you'll find is that instead of a small number of obnoxious teenagers with a liberal world view making obnoxious comments you'll have a small number of obnoxious teenagers with a leftist world view making obnoxious comments.
People also claim that moderation is an issue on some communities, but hey, it's all federated, jump across elsewhere.
Hatred for lemmy.ml is just an echo chamber quirk.