Using a Space Hammer could quite possibly be a global suicide scenario because of all the debris it would kick into the atmosphere.
Somehow I don’t think we’re going to beat St Helens on the debris/atmosphere front.
The Earth gets hit with about 400 tons of meteors/day. The space rocks we drop on our enemies don’t have to be megaton range. A guided reentry vehicle with 50 tons of rock would wipe out an underground Iranian nuke facility with minimal damage on the surface.
Dropping a few rocks on the bad guys will not cause “nuclear winter”.