It boils down to this — would you allow businesses to discriminate against and deny service to black people for being who they are? There was a Supreme Court case back in the 1960s called Heart of Atlanta Motel that said, in effect, that private businesses could not deny service to black people.
https://en.m.wikipedia.org/wiki/Heart_of_Atlanta_Motel,_Inc._v._United_States
Gay people are no different. Like black Americans, they are a “protected class” that has faced historical discrimination, hate crimes, and ongoing harassment for being who they are.
Some religious people cite the Bible. Well, it’s not a great text for the modern world. You can find all sorts of crazy things in the Bible. Confederates used to use the Bible to justify slavery. The Bible has murder, incest, infanticide, and genocide in it — and doesn’t always clearly disapprove of those things either.
The most important passages of the Bible are what Jesus said. And He taught love, tolerance, and acceptance. He didn’t explicitly say “love and accept gay people,” but the thrust of His teachings point in that direction.