I think you meant to say "Sprint". In any case, if you're being attacked I think the consequence of high altitude fallout is pretty small compared to dying.
Depends on what you're being attacked by. If it's just regular warheads, a nuclear interceptor is wildly inappropriate especially if the intercept happens over someone else's airspace.
That's better but people typically won't appreciate a thermonuclear explosion overhead in order to take out a missile armed with a few hundred kilos of explosives. That is doubly the case if the nuke is from a neighboring country intercepting a missile targeting them.