Republicans have been calling democratic voters baby-killers for the entire time I have been aware of what a republican is. This sort of behavior has only gotten worse over time. They still manage to win elections.

I get that there are real asymmetries here, but I really don't think there are substantial blocs of swing voters who use "who has insulted them less" as a real factor. If that were the case, Trump would not have made the gains he did in 2024.

The important thing is to make people feel welcome in your coalition. It is clearly possible to do that either with or without being nice. It's just a different skillset.