I'm OK with the deletion of very-short-lived copies of myself if there are good reasons to do it.

There's a very nice thought experiment that helps demonstrate this (I think it's from Nozick). Imagine a sleeping pill that makes you fall asleep in thirty minutes, but you won't remember the last fifteen minutes of being awake. From the point of view of your future self, the fifteen minutes you don't remember is exactly like a short-lived copy that got deleted after fifteen minutes. It's unlikely that anyone would claim taking the pill is unethical, or that you're killing a version of yourself by doing so.