The disagreement between anarchists is, while the state exists, whether some state enforced border controls can be preferable to none at all.

I believe some such controls can be preferable. In the sense that there is likely to be a set of such controls, for every taxed population, that minimises injustice (beyond the injustices the state already creates).

Here's the idea: The indigenous population have preferences about who they wish to associate with. And who they would allow into their territory, if they were not ruled by the state. The closer the state border controls approximate the wishes of the subjugated population, the less injustice exists. By enforcing border policies that align with the preferences of the victim population, partial restitution is being given to that population. Which is better than no restitution at all.

I call it the argument from imperfect restitution. Kinsella put it like this:
https://www.lewrockwell.com/2005/09/stephan-kinsella/a-simple-libertarian-argument/

Your post calls people who find this argument compelling 'immoral, fearful idiots' (me included) but hasn't addressed it.