Isn't even simpler than that? You are not them.
Exactly. Government intervention that benefits them and their positions seems to be fine (especially if it requires other people to support their positions); government intervention which does not benefit them directly - even if it benefits society in general - is evil and oppressive and must be abolished.
Of course, conservatives also accuse liberals of using the legislative process to force them to support liberal causes - and they're right; it's pretty much an unavoidable outcome in a two-party system. I don't think it matters whether the legislation is proposed by a liberal or conservative; the real test should be whether or not it is consistent with the principles of the US Constitution.
In the case of the gay marriage debate, passing a legislative or constitutional ban perpetuates a structural inequality that creates two classes of citizens - those who enjoy marriage rights and those who do not; granting gay citizens access to marriage rights corrects an existing structural inequality and thus is consistent with Constitutional principles. So in this case, the liberal cause passes the test and the conservative one does not. Argue all you want about whether or not marriage should be about procreation, but the fact is, many of the marriage rights have
nothing to do with procreation whatsoever (i.e. survivor partner benefits, visitation rights) and therefore should not be dependent on a procreative union for access.