People are focused on the bathroom part of the bill because that's what's in the headlines, and let's face it- it's a stupid law because there's no way they're ever going to enforce it. Are they going to ask people to produce a birth certificate in order to enter a restroom? But the bill is also about something far more important- it prevents municipalities within the state from passing laws that prohibit discrimination. For example, it takes away the right of a person to sue if they are fired from their job based solely on their sexual orientation.
Andrew, you state that you "can't stand" religion, which is your right; the Mississippi law allows businesses to deny services based on religious grounds. As such, opposition of the law seems in line with your own views (IMO).
As far as other artists or businesses "jumping on the bandwagon", that's the whole point. This is in effect an economic boycott. If someone doesn't put a foot down at some point, it can become a slippery slope. Steve Van Zandt spoke about this a few days ago: