I'd never heard of this ABO stuff before. I find the concept of genetic ubermensch* who are natural leaders stupid and offensive, so I can understand why it would be widespread on the internet. I like a lot of Takemiya Jin's stuff, but, sigh, it doesn't really surprise me she'd get into something like this. Hard nope for me, I like her stuff, but I don't like it THAT much.
*Yes, yes, some of the "mensch" are female. Doesn't change the concept.