Failing to do so results in the process crashing if the operation hits a prepare conflict. This is a rare occurence, which means we risk not catching crashing bugs in testing. In addition to the visual clutter, the API risks that developers create new internal threads that are unkilllable when they shouldn't be.
It seems that there are only a few system operations that actually need to be unkilllable and the vast majority of all threads should be killable.
We should consider changing the default such that system operations are always killable and have the limited set of special operations explicitly opt-in to being unkillable.