First things first: if you want to be a Christian and happen to believe that a gay lifestyle is not for you, fine. I am not here to object. Everyone should have the right to their own religious beliefs (or non-belief.) Everyone should have the right to determine their sexual orientation on their own and without outside involvement. The mere fact that I have to explicitly say these things boggles my mind.
Now for the other things: What we do not have the moral right to do is to impose restrictions on others who may, or may not share our religious views. This is oppression, especially when it is a majority applying restrictions against a minority. It is oppression to put forward a law that restricts others outside our community in ways that don't apply to ourselves. It is oppression to bully corporations who don't actively support these laws or beliefs. To boycott Starbucks is to actively punish a corporation because they actively stood up in support of basic human rights and equality for all.
To boycott Starbucks is to put yourself on the wrong side of a human rights debate. To boycott Starbucks is to illustrate a measure of hypocrisy, since Christianity is, at least on the face of it, supposed to be about forgiveness, acceptance and love - and this action is none of that.
Anyway, enough ranting. I need a coffee.