On the other hand, asteroid mining technologies have some risks of their own, although this only reaches "existential" if somebody starts mining the big ones.

The largest nuclear weapon was the Tsar Bomba: 50 megatonnes of TNT, roughly equivalent to a 3.3-million-tonne impactor. Asteroids larger than this are thought to number in the tens of millions, and at the time of writing only 1.1 million had been provisionally identified. Asteroid shunting at or beyond this scale is by definition a trans-nuclear technology, which means a point comes where the necessary level of trust is unprecedented.