It's different because that judge is not marrying anyone, straight or gay. Since gay marriage is still illegal in Texas, she can't marry a gay couple and then tell straight couples to hit the bricks. That court clerk is still signing marriage licenses for straight couples, but not gay ones. This is a dereliction of duty and she should be fired for it if she doesn't agree to do her job.
Christian apologetics is the art of rolling a dog turd in sugar and selling it as a donut.