To oppose homosexuality is to oppose love. To oppose love is to oppose god.
The love God has for someone and the love one should have for God, is much stronger (and is quite different) than the love people experience with each other. (from a religious perspective)
How can you claim to love god when you hate what god created? Why should god accept you when your heart is full of the most impure of all feelings?
Hate the sin, not the sinner