Situations that call for weapons are highly variable. There are lots of use cases in which high-capacity semiautomatic firearms are the most suitable. Some of those absolutely are self-defense scenarios.

It's rather a moot point at this juncture, though. There are literally millions and millions of such firearms in civilian hands in the US, probably more at present than there are "Fudd" guns like revolvers, hunting rifles, and shotguns...and they're not going away. Policy has to reflect that reality.