I don't think anyone cares about Christians being offended. Source: most pro gay marriage posts on BoS.Furthermore, we have this oversensitivity to religion where we "can't do anything that might upset them" - namely Christianity because of it's prevalence in our society - for example, we can't legalise gay marriage, euthanasia, abortion etc. because it might offend the Christians. As a society we are too familiar, comfortable and sensitive to conservative Christian values, which does inhibit social progress. And because of our heritage stemming from Christian values we place a lot of value on asceticism which inhibits individual fulfilment (drug and alcohol laws, sex laws such as age of consent and statutory rape).
The point is that more votes are won by shunning gay marriage than introducing it.
For those who support it, it is not as much of a game breaker.