I've seen a few people in online HE groups complaining like the OP about these "oddballs", conspiracy theorists, freemen, magna carta, etc but I've rarely seen any of these people either online or irl, except maybe once or twice in one or two posts related to laws, etc, and I've been HEing for years. I only see people talking about them once they're brought up.
I imagine if you get nasty posts about not being welcome with mainstream views, you're either in a group with rules mentioning they only accept non-mainstream views or you report to the group admins who would quickly remove the post/poster if in the regular HE groups.
I honestly never know what to make of these claims of "seeing these types of people and posts everywhere in the HE community" but it could be that they really are zapped quite quickly - and if so, it shows that these are rarely allowed and are not everywhere - or relegated to niche groups where I assume they're not just "Home Educators" but other things that are non-mainstream like Homesteaders, Preppers, etc and/or stuff like that. So they really aren't what you'd call Home Ed groups, I'd say.
I also ask to know where to find these people out of curiosity but I never get a reply. Lol Just like pp have asked the OP what groups these are and no reply yet.
I'm sure there are people with different views who HE their children as well but that is the beauty of HE. There's space for everyone. As long as they aren't forcing others to join their group or think like them, it's alright and their business.
As you've left the groups now, that should help with not seeing them, I suppose. I suggest you join the regular national HE groups and your regular local HE groups. A lot of them are connected to each other.