I've got friends who say things I disagree with, they're not assholes. They're nice people with different views. Some people say things I agree with, but at the end of the day, they're still assholes, even though we share some opinions.
Any group large enough is going to have some assholes.
If you get called toxic a lot, it's not just because people disagree with what you say, it's probably how you're saying it.
Further, maybe you're not an asshole in every group, maybe your (and I'm using the word "your" here in a general term, I'm not talking about anyone specifically) personality just doesn't jive with the rest of the group, making you the asshole when you just have a personality which doesn't fit with the group which makes you toxic.
Take for example a subreddit like /r/aww which is just idk, cute photos. Someone who comes to that community and points out flaws, or seems to need to point out problems with the posts, content of posts, etc, well maybe they're toxic to that community, since it's just one of feelgood-ness. It's not that they're a bad person, or have bad opinions, they're just not behaving in a way which seems appropriate for the group.
The claim was the complete opposite that almost any objectionable behavior is labelled as "toxic".
It is hence about as undescriptive as "liberal" is in American politics. That term many years ago had a well-defined narrow meaning but is now far removed from that (or like "literally" often meaning "figuratively" in common use ).