This is our disposition in the West

So, in accord with this:

http://timesofindia.indiatimes.com/world/europe/german-parliament-legalises-same-sex-marriage/articleshow/59384179.cms

we in Canada agree.

However, for the Mohammedans, their disposition is that:

homosexuality entails an unnatural act!

So, how can you frame a sound logical argument to prove them wrong?

I have thought about it and I not able to tie it up.

Can you help please?