There aren't really as many leftist posts on lemmy.ml from what I can see, but it's federated with lemmygrad.ml, so if your account is on lemmy.ml you see all the posts from there as well. And because they're federated, lemmygrad users can comment on anything on lemmy.ml, so that's where you will see viewpoints come in that you may not agree with in news/politics/economics related threads. I don't know if kbin.social has its instances whitelist & blacklist published anywhere, but there's a pretty good chance you'd know by now if it federated with lemmygrad. You're likely still browsing posts and comment threads on lemmy.ml but aren't seeing comments from the lemmygrad users in those threads.