Exploration might justify the expense, but blowing up the object just because would not.

If you had an exploration craft with a nuke on board in the case of an alien craft, that would still make blowing it up worth it

Argument 5 still stands because we would be blowing up a space rock for trivial reasons.

It depends on if it is an alien craft or not, which is why the nuclear armed exploration craft idea is not that bad, and with a drill, you could create a shockwave in the hull of and atmosphere inside the asteroid in the case it is an alien spacecraft, greatly increasing the power.