lastdan:

what I really don't understand is why anyone would think that allowing 'Same-sex marriage' will in any way change non-Same-sex marriage.

If “marriage” is defined as “an exclusive union forged between one man and one woman” then “same sex marriage” becomes non-sensical. This is the reason most people opposed to same sex marriage object to it: the concept necessarily changes the definition of the word “marriage”. The same issue would be raised if marriages with multiple partners were in question.

what happened to the no church / state thing?

Well marriage is already a church/state thing. It’s clearly a religious institution (at least in many cases), but it’s also a union recognized by the state for legal purposes. With the same sex legislation, religious intuitions are feeling like the state is stepping on the church’s toes by redefining a religious term into a secular one.

Bitt:

One thing I'm unclear on is there seems to be a difference between ``civil union'' and ``marriage'', and I don't know what it is.

The difference would be that a “civil union” has no pretext of being religious in anyway; it is merely a legal union useful for determining what rights coupled individuals have together.