US atheists/left-wing people, how do you feel about Californian cities and towns having Christian place names and if they had Islamic names, might

Historical names are just that. I don't think the name changes whether a town is worth visiting or living in. Maybe if the proposal was to just start renaming things to seem more Christian by association then that would be weird. Renaming things with Islamic names would also be weird.

I honestly don't think most tourists care about the city name. They care about what there is to see and do there