Why do secularists feel so passionately about the use of reason when it comes to making informed moral decisions? Because our moral values and laws should be based on the most informed, most pragmatic, most practical and rational, and the most scientific and evidence based reasons that are humanly available. They should never be solely based on what has traditionally been done or believed, or what a certain book believed to be divinely inspired says, or be based on some strict ideology exempt from criticism and reform.
The Supreme Court of the United States is taking up the legality of the Defense of Marriage Act (DOMA) and the role of states and the federal government on gay marriage. It is amazing how fast public opinion has changed on the gay marriage issue. The issue first confronted me back in the summer of 2004 when president George W. Bush was running for reelection and it was the hot button social issue. At first I wasn't sure about it. It seemed kind of weird to me. But this was only because I had not really thought about it at all prior to that time and I was making a judgement purely on my emotional reaction to it. Over the years I warmed up to the issue of gay marriage as I became more educated on the matter and of sexuality in general.
I just recently saw a debate between Pastor Doug Wilson and columnist Andrew Sullivan entitled "Is Civil Marriage for Gay Couples Good for Society?" Andrew makes a very emotional opening speech and Pastor Wilson essentially makes the slippery slope argument basically saying that if we allow gays to marry today, Muslim polygamists are going to demand to be able to marry 4 wives tomorrow.
Although there is no evidence that this is the case at all, the main rebuttal Andrew presents is that polygamy is not a state, it's not an orientation, same sex attraction is. Polygamy is therefore a preference, it's not a sexual orientation; no one is born needing 2 or 3 wives. A man may wish to have more than 1 wife, many men do, but a polygamist gets to have at least 1 spouse where as a homosexual would not be allowed to have one if current discrimination continues. That's the meaning of equality: gay people just want to be equal to their heterosexual counterparts. And finally, if a man can have 4,5,10,20,or 50 wives, it upsets the male to female balance ratio making it harder for other men to find wives.
There are still a great many number of religious conservatives who believe that homosexuality is a choice, like the way going to Baskin-Robbins and picking out an ice cream flavor is a choice. They think all gay people are really just straight people who are just tempted by sin. Their ill-informed religious worldview just won't allow them to accept that gay people are born the way they are, and so they'll say things like, "There is no gay gene!", and "There are ex-gay people who have been made straight by the power of the lord!" And of course I naturally have to laugh in response to such confident nonsense. Even if there isn't a gay gene, to anyone educated, sexuality is obviously a complex arrangement of hormonal influences in the womb and neuro-physiological development of the brain.
But while on the slippery slope argument anti-gay marriage proponents seem to love making, let me address a few of them briefly.
Pedophilia - underage children are not old and mature enough to make the kind of important decisions like consenting to a marriage requires. In cultures where children are allowed to marry, it is often their parents that arrange it for them whereby the child has no say in the matter. Consent requires a person of legal age and most scientific research deems that age somewhere around 16-18 for most people. The same goes for sex with children. Pedophilia harms children and takes advantage of them, that's why young children are not able to consent to sex.
Bestiality - animals also cannot consent to marriages and are also in the same class of vulnerability as children are when it comes to sex. Marriage allows such things as the power of attorney amongst spouses and that role cannot be fulfilled by an animal. Can you imagine a lawyer having to deal with a horse or a dog when dealing with a divorce or its spouse's death? There needs to be a human recipient who can give a civil consent in such legal matters. A human being can own an animal, but there is simply no need for them to be married to the animal since all the legal benefits of marriage have no practical application between species.
Think, understand, and form judgments by a process of logic. That's the definition of reason. It is very hard to make the case against gay marriage if you cannot appeal to religion. But in a secular democracy like ours we champion individual liberty, equality and freedom of the will so long as it doesn't hurt anybody. Gay marriage harms no one, and the slippery slope arguments made by dissenters are unfounded and fallacious.