Now, to be clear, I am not questioning the right to spread this nonsense. I understand freedom of expression and its importance. But just because something is lawful that does not mean it is right.
Freedom of expression can't support itself alone. It must be coupled with responsibility for what one expresses.
Promoting the opinion that homosexuality is wrong, shouldn't be acted upon, or is unlawful and/or sinful causes harm to real people, therefore it is wrong.
It is really a very basic matter of civil rights and respect for personal dignity, that comes before, above and beyond any considerations for law, religious doctrine or cultural tradition. One ought not to find hurting others too normal. That's very much the essence of it, and the deciding reason why homosexuality ought not be spoken ill of.