Maybe it would be nessecary to divide between marriage by church and marriage by state?
As with thinks like other taxes for marriaged persons, or the right to visit the partner in a hospital, it is no more some kind of "religious only" thing.
If a catholic beliefe that a homosexual will burn in hell, and shall not be married in a catholic church: sad thing, but.. okay... house rules. (Going just as far as somebody has to suffer, so: NO EXORCISM!)
But: Why shall catholic interferre in questions regarding the legal questions, like:
- visiting in hospitals
- adopting children
- taxes
It is out of their house.
But here comes the point: They tend to demonstrate against things they just could ignore...