It's much bigger. It's about who we are, and who we want to be.
I would be very happy - ecstatic - if Haley won the GOP nomination, even though she would probably beat Biden handily. I would strongly disagree with her policies, just as you strongly disagree with Biden's. But that is normal disagreement, inside the normal scope of American politics.
Trump is outside that scope, and a danger to the system itself. A vote for him is a vote to weaken the republic, and once it is weakened, it is hard to make a republic strong again.