Listening to all of the rhetoric that surrounds the gay marriage debate today, it's interesting that the focus of those who accept it, at least the ones speaking most loudly today, seems to be on what makes people happy.
Now, this is the goal of the unbeliever. It is the goal of every self-worshiping religion on the planet, which is every religion beside historic Christianity. What one sees as the ultimate goal in life will ultimately dictate what behaviors one finds acceptable (that is, if he or she is consistent).
If the goal of life is to be happy, then you can fulfill that goal through any means necessary. If homosexual activity makes you happy, then go for it. If leaving your husband and children to pursue a new adventure in life makes you happy, then happy journeys. If drugs and alcohol make you happy, then shoot up, drink up, or shut up. Whatever makes you happy.
Worship the god you want, have sex with the object you want, take whatever you want, or give to the poor if that makes you happy. Whatever. If the ultimate goal is happiness, then these people can continue to argue this way, but if we all know that such would be wrong, then we need to ask whether it is true that happiness is the ultimate goal of life.
And we all know that it is wrong. I can't murder because it would make me happier to remove certain people from the world. I can't go on a stealing spree because I want everything to make me happy. And I can't just seek whatever sexual relationship I think might make me happy.
Why? For two reasons really.
The first is that we are under a sin-induced delusion that teaches us that happiness is to be found in things that are actually going to leave us unhappy in the end. We're are told that ultimately, only having a restored relationship with the God of the Bible through His Son, Jesus Christ, is the key to our happiness. So our delusions, ironically, lead us to pursue happiness in death.
But second, the ultimate goal of life isn't our personal happiness. It isn't the stimulation and exaltation of the self over others. The ultimate goal of life is to worship and exalt God by glorifying Him in our life choices. This, ironically, in return does bring us happiness, as love of God rejoices in His glorification and honor.
Because of these two things, the question can no longer be, "Doesn't this person deserve to be happy?" or even "If it makes me happy, why can't I pursue it?" Instead, it must be, "Does it glorify God in the truth He has revealed by loving Him and others over myself?" "Does it kill the Self in order that Christ and His Word might live in me, so that I might glorify God?"
If this latter trend is the line of questioning rather than the former, then you cannot argue for your alcoholism, drug addiction, murder, sexual abuse, false religion, neglect of your marriage and kids, or homosexuality as being rooted in the pursuit of happiness, as it is obvious that such is not the ultimate goal in life, since if it were, all of these would be legitimate pursuits, regardless of what oppressive laws or societal taboos might say contrary to the matter.