Technically, marriage IS strictly between a man and a woman. No man can marry a man and no woman can marry a woman.
It's called civil partnership, so technically they're not getting married, so technically it's not against religion.
mirite?
Depends what you view as marriage, and even then like Pyru said, they still don't have exactly the same benefits.
Besides, Religious Marriage and Legal Marriage are completely separate things nowadays. They may have started the same, but that's irrelevant in the modern world: They became separate entities when church and state became separate entities.
For the former, I say it's up to the religions beliefs and beliefs of the vicars/ministers/whatever involved.
For the latter, it's a contact, nothing more. It's there to protect those who marry because it traditionally involved leaving one career "for the family", and as much as some try to deny it,
on average one of the partners in a marriage relies on the other to earn the most money, and without this income could not live the life they lead.
This means some legal protection is required, in the event the person they gave up their career for dies, they need protecting. Now, this protection should not extend to people based on whether it's a man and a man or a man and a women or a women and a women, it should extend to all such couples or none at all, anything else cannot be justified. This doesn't subtract from the meaning of marriage, nor the wonder, it simply makes society as a whole
better.