[layman]

Churches that oppose same-sex marriage legislation have good reason to fear for their charitable status

Why doesn't the gay community, instead of trying to destroy traditions which have evolved over many centuries, start up their own church and apply for tax exempt status. They could elect their own Grand Gay Guru, design their own gay wedding ceremonies, and maybe even come up with some traditions that the straight community never even thought of. The truth is that we're not all the same and the straight community isn't interested in denying rights to the gay community ... what we're interested in is protecting the institution of marriage. Start your own church ... leave us alone.

[Heartofsong83]

They already have that. It is called the United Church of Canada and the Metropolitan Community Church.

[GMMAC]

Churches losing their tax-exempt status really isn't the central point.
In fact, it might even be argued in the case of some the fatter and more smug ones, that it would compel them to re-adopt more historically authentic Christian attitudes and practices in a few areas.
However, the primary effect of losing this status would be to weaken them as a moral force and they're currently the main entities opposing the left's efforts to destroy the conventional family, impose its companion pro-decadence agenda and stifle our fundamental liberties.

Bottom line and theology aside: if you value your conventional family and your personal freedoms, back the traditional Churches.
It's no accident that the freedom-loving founding fathers of America were also all devout Christians.