The difference between the US and the UAE is that the latter has no diplomatic relations with Israel, and in fact refuses to recognize Israel’s right to exist. Given also that Hamas has declared and is conducting a war of annihilation against Israel, and that presumably the UAE is supporting the Hamas side of that conflict, I don’t see why Israel is obligated to make nice with them. Equating the assassination with one in the US is a red herring, even given the assumption that Israel had anything to do with it in the first place.
I have no diplomatic relations with the hillbillies down the road.
Does that make it fine and dandy if I go cap a few of them?
Even if they have a meth lab or a dog-fighting operation?
The "badness" of the target does not exonerate the assailant.