it’s valuable to criticise Christians who act in a deeply unChristian manner

It's hard to talk about being "unChristian" when you're describing a faith with this many schisms. Most Christians can't agree on what qualifies as "Being Christian". So an outsider looking in, with only a superficial understanding of the high notes of one particular sect, is going to have an even worse time of it.

However, pointing out the hypocrisy of Christian settler colonialism is one of the ways we can assert that it’s not the Christianity that’s the problem

I mean, I can point you to Mormonism as a sort-of twisted web of problems. On the one end, you've got some clearly made up bullshit. On another, you've got one sect of people believing made up bullshit conducting pogroms against another. And then that ousted sect runs off into the American Southwest to do pogroms on American Natives in turn.

And all this echoes the original flight of Protestants from the Old World of Europe in the wake of the 30 Years War. It's easy to say "Well, obviously, the problem is religion". But the problem isn't any one sect of Christianity, or Christianity as a whole, or even religion as a whole. It is an effort by powerful people to force the their weaker neighbors to conform.

The cycle of heterodoxy and homogenity - the Hegelian Cycle of change - is what drives conflict between tribes of people and determines their behaviors over time. Reconciling conflicts between tribes must require some degree of rational coexistence. It can't just be a new pogrom against the old crowd in the name of historical wrongdoing.