I find it remarkable that anyone thinks they have any right to tell people what they can and can't do with their own bodies, especially in private with another consenting person!
That said, it may not be because this pastor is a really hateful person (although it's more probable than not), but because he genuinely believes that his god hates homosexuality, as written in the Bible, and wants to please his god.
Either way, his actions are disgraceful and inexcusable!