Is this just about votes?

Politicians are thinking about the legalization of same sex marriages as possibly being a blow to their elections. Some politicians are against the same sex marriage bill because of the amounts of votes they stand to lose. So what, does this mean that MPs are going to throw away the idea of a same sex marriage simply because of what THEY could lose? I wondered if these politicians have thought about what couples in a civil union stand to lose? When it comes down to it, couples in a civil union means nothing when their other half has been involved in an accident and why? Because in a civil union, your not classed as immediate family.