A very tiny minority of Buddhists would think about moralising on someone's private behaviour. Mind you, I'm sure there are a few Evangelicals in favour of SSM too. I know an awful lot of gay Buddhists of all traditions, even Tibetan.
The highly respected and influential Zen master Thich Nhat Hanh was asked...
Even the Dalai Lama, known for his somewhat retrogressive views on homosexuality says he..."opposes violence and discrimination based on sexual orientation. He urges respect, tolerance, compassion, and the full recognition of human rights for all."
Here is a terrific article on the
Buddhist attitude to sexual ethics. It would be well worth reading it all, but one passage stood out in the context of this thread: