The TL;DW is that leftists have never been unified, and never will be. We all have our differing goals and preferred means. Rather than trying to browbeat everyone into falling in line under a single unified ideology/party/platform/etc, we should just collaborate selectively on a per-project basis, and otherwise not worry about it.

That sounds like Max Stirner's "union of egoists". Work with others when doing so helps gets you what you want.

Tankies are allergic to this notion, though.

Not just tankies. Try telling a social-justice type that the only identity you give a shit about is class identity. It's hilarious.