Problem is, I DO have interactions, in real life, with that kind of people. And there's nothing but trying to get them to get help that I can do.

And you might not have much contact - because I've seen otherkin be as vehement in their doing as the extremist feminists (one is "Kill All cis-species freaks" and the other is "kill all men"). And I've seen parents raise their children that way. And of course they can believe what they want to believe - it does not mean it's healthy, just like you shouldn't encourage someone with split personality to develop both, or to encourage someone with bipolarity to embrace both sides of their trouble instead of seeking help. Hell - we already treated people for mental illness because they thought they were other people - what makes people who think they're animals (and by that I don't mean people who have a spirit animal or really look up to an animal - I am talking about the "I am an animal stuck in a human body" folks). And I know I look like an asshole - but it's not like "You're mentally ill, get some help freak" but "You have mental troubles - please, for your own sake, get help before something worse happens". Like telling someone depressive to seek help before they turn suicidal, or a person afflicted by psychosis to get help before they're arrested/killed during an episode. As for understanding them - I don't claim to completely get them, but from an objective point of view, I can understand the reasoning behind their beliefs - however it is not healthy (as most point of views is some variant of "humans have done terrible things, therefore all humans are terrible, and since I am not terrible I cannot possibly be human").

And no, I don't understand how silly it looks simply because I mean no ill. I do not oppose the ways of living - I oppose the reasons for the ways, and the extremist beliefs that sometimes come with it. The group I am talking about has an unhealthy hatred of the whole human species. Just like I oppose extemist feminism who has an unhealthy hatred of the male gender (and sometimes all genders except purely feminine - no natural or operated trans-person (F2M is "gender traitoring" and M2F is "infiltration"), and so on).