I'm very much on the Left and always have been. But I'm old school Leftie, a believer in material reality etc.
That's very different from the modern "progressives" who are obsessed with identity politics.
To me, the omnicause is summed up by the chant, which I have heard many times from people who believe it:
"Palestine,
Trans rights,
One struggle,
One fight"
Two completely unrelated issues which are shackled together for reasons that make no sense. The fact that there's a group called Queers for Palestine when Hamas would throw them off the roof of the nearest building if its members ventured into Gaza completely baffles me.
The omnicause is a handy word to describe people who will take a Palestinian flag and a trans flag to any demo or march, no matter what it's about.
FWIW, I have been sympathetic towards Palestinian people for many years (the film Mayor is a really good portrait of what life is like for ordinary Palestinians trying to lead a normal life), think that the destruction of Gaza and the actions of illegal settlers on the West Bank are indefensible.
But I also believe that the October massacres carried out by Hamas were abhorrent atrocities and that the state of Israel has the right to exist.