Bible-believing Christians will still support their churches, tax exemption or no. In fact, the more willing the church is to vocally defend biblical morality, the more willing believers will be to support it.
The issue will soon cut past “biblical morality.” It will reach that of sin and Savior.
As long as we are stopping at morality, we are really concerned with how nice life on earth is.
It’s a gift. You can give gifts to anybody you want.