There are a multitude of reasons why people need access to semi automatic weapons [View all]

With large magazines that allow them to shoot 10+,20+,30+ rounds without reloading. Here are those reasons:

Zombie rampages. It takes literally hundreds of rounds to even slow them down. A semi automatic weapon will buy you enough time to escape to the safety of an abandoned mansion.

Red Dawn. There have been multiple versions of this, but in each, it was a few heavily outnumbered gun owners that defeated Superpower militaries who attacked America.

Post-apocalypse hunting for those with poor marksmanship. People that can't shoot need to eat too, let's give them a chance.

I may have overlooked some other reasons, but I think these are the primary ones.