A) That being LGBT is a choice. It's not. There is not one single gay or trans person in my life that would have chosen to be a minority that is regularly the object of hate and violence. I've seen friends beaten, and then treated like they're not worth the police department's time. They've had bottles thrown at them from passing vehicles, simply for walking down the street in the gay section of town. Who the heck would choose that?
B) That there is an LGBT "agenda" that is being rammed down everyone's throats. The real agenda is to have equal rights, and equal protection under the law. There is little protection for LGBT people in most areas of the south. People can be fired when their boss discovers they're gay, and turned down for jobs completely simply because they're trans. People can refuse gays service, and say horrific things to them while they do so. The agenda is to make that stop.
C) That LGBT people are not "like us". They are EXACTLY like us. They grow up, go to school, get married, have children, and pay their taxes. They go to church. They join the PTA. They are not simply the people you see in the gay pride parade, any more than all straight people are simply what you see at a strip club. They are us.