I get that garbage too.
This idea that there was ever a universal Christian way of doing things in this country is insane and incorrect. One needs only look back to the people who came to America to flee other Christians who persecuted them. Or back to the controversy of JFK getting elected - as a Catholic.
It's a wedge issue. It's essentially supporting people's prejudice (because it supports their prejudice, they won't look at it too hard), giving it a religious coating, affirming that "Yes, you aren't a bigot, you're a wonderful person for hating gays," and tying it to a particular political party. It's not that different than other wedge issues. It's designed to fire people up ("YOUR CHILDREN WILL BE EXPOSED TO GAY!") to get them out to vote for the "defender of the faith," which is whatever closeted gay politician that is running as Republican at the time.
(Oh, the Democrats do it too - they just pick different issues)
But I'm *REALLY* wanting to sponsor a ballot initiative to bring back the Biblical definition of marriage. If I had a funding source, I'd do it (I need signature gatherers!). Essentially, "Amendment to amend constitution to include 'Marriage is defined only as the types of marriages the Bible supports as god-sanctioned.'" If these right wingers want Biblical marriage, I say go all the way: Polygamy (one man, many women), child marriage (well, we already have that in New Hampshire - 13 year old girls and 14 year old boys can marry, unless they are gay in which case they have to wait until 18), cousin marriage in all 50 states (it's recognized everywhere today, but not legal to enter into everywhere), and no divorce except for Biblical reasons (which don't include spousal abuse). If people want Biblical marriage, that's what they should get - not this watered-down one man/one woman stuff.