Government inherently imposes morality on its society. Laws define what is morally acceptable and unacceptable, and the enforcement of those laws in turn constrains society to the particular aspects of morality manifest in said laws.
A democratic society should theoretically have laws that represent the morality of its population. Things get a little trickier with representative democracies like the United States. While the United States has a complicated and nuanced system of government, I think we all agree that its laws should be supported by a large portion, if not the majority of its population.
So, for the sake of simplicity, let's presume that this idea (that a democratic society should have laws that represent the morality of its population) holds for all democracies, direct or representative. The people vote for laws and policies, or elect individuals to govern, such that the resulting government matches their own values as closely as possible.
To recap: anything relating to the governance of a society is a moral issue. This includes the definition of rights. The problem with moral issues is there is no right answer, except through consensus--that's just the way we work. A philosophy is only as good as its strength in obtaining adherents.
You see, moral issues, while the can be argued logically, are predicated on some premises, which, when you get to the core of things, have an emotional basis. A good debater can construct an argument to prove anything given the right set of premises. That same debater can also dismantle any argument if allowed to disregard or redefine the premises.
So what does this all mean? Let's consider an example: the laws and rights pertaining to marriage, which seems to be such a popular topic these days. Some people have the emotional premise that marriage should only exists between and man and a woman. Other people have different emotional premises that lead to the conclusions that marriage should be able to occur between any two willing adults. There are also folks who think marriage shouldn't exist as a government construct, based on the premise that government should be minimal. There are many more variations in opinion and other complicated aspects like rights outside of marriage, but I'll leave itemizing all the permutations and complexities to you.
How do we decide what to do as a society in the US? We vote, courts make decisions, laws are passed. In the case of courts, judges have a set of legal premises in addition to their own options. Again, it's a complicated system, and in the case of same-sex marriage, there are strong opinions in either side.
I believe that same-sex marriage will be legalized eventually, since the primary purpose of modern marriage is individual fulfillment. (There are more personal premises and opinions related to whether or not that should be the case.) The question is whether it will happen at the state level or the federal level. In general, I'm more in favor of state level laws, but there are tricky questions regarding recognizing marriage from other states.
What I really wanted to drive home is that when people make arguments that seem totally illogical to you, it's probably because they have a different set of emotional premises. (Though it's entirely possible that they have faulty logic.) I've read many articles about how there are no good arguments against gay marriage. Of course there aren't if you don't share your opponents' premises! Opposing same-sex marriage is hard in particular because there is no argument: the opinion is the premise. Proponents, on the other hand, can dig for deeper premises relating to equality, and thus make more compelling arguments.