If I ran a company and had LGBTQ employees, I would not want what you just described because it would be creating a hostile environment for those employees.
Coming into your workplace and telling your co-workers that they don't deserve equal rights under the law is just a shitty thing to do. It's an issue of basic respect and has nothing to do with politics.
There is no harassment when someone simply states "I don't think same sex marriage should be legal.". And before I get downvoted into oblivion, I don't agree with that statement, I'm actually completely apathetic to it and think it's unimportant.