“Why attend a beis minis instead of going to a actual Jewish school,it’s assur to daven in a place with a Israeli flag and questionable if one may enter at all,so why attend such a heretical place?”
I think that is only if you are Satmar. I am pretty sure that there have been completely acceptable places that have had the Israeli flag for whatever reason, and very shtark people davened in these places.
Imho, you should not make blanket statements stating that something is assur unless you know that it is completely true according to all acceptable opinions and can back it up with sources. I actually would be interested in knowing if you have a source for such a statement.
That being said, I agree that one should not davka choose a school based on the fact that it is zionist.