So, if I'm understanding you correctly (and please correct me if I'm wrong)...

"Horizontal aggression" is more of a social and cultural problem, and rarely systemic.

Heteronormativity is widely systemic, as well as having the ability to spill into the social and cultural realms.

All of the above, I'd classify as "orientationism" (discrimination based on sexual orientation), but the context is what differs.

So then, within the LGBT community itself, another form of horizontal aggression could be the glib and thoughtless (mis)usage of the term "genital preference," insofar as passing judgement on other people's romantic lives. Although that could warrant its own separate article...

But your core point appears to be that all of us who are part of the LGBT(+) community, across the spectrum, should support one another? In terms of that statement, I'd agree 100%.