Why tradition is not a good thing, such as opposition to gays
Is tradition a good thing? Or, to rephrase the question, is something good because it has a lot of tradition behind it? Well, many good things have lasted because they are good and hence became a tradition.
But, are traditional beliefs, institutions or events good in of itself because they are traditional? Of course not. The reason why anything is good is because it has some value to society, the individual, the culture.
For example, a traditional moral value in all cultures is a prohibition on murder. This value exists not because it is old or traditional, but without it society would become unstable and violate the rights of individuals in that society.
So the reason that we prohibit murder or rape or theft is solely based on the merits of the harm that they cause. One doesn't have to appeal to tradition to state why these things should be illegal.
But, there have been bad traditions: slavery, divine right of kings, denial of women the right to vote, etc., so tradition by itself own nature isn't an indicator why something is good or bad, so one is forced to look beyond tradition.
Indeed, of these evils that I just named, all have been defended, with great emotion, by appeals to tradition and all have fallen by the wayside with time. Would anyone argue that every bad or unjust tradition that existed no longer exists?
Probably not, though the great evils of bad traditions such as slavery are no longer the norm (at least in Western society), lesser harms still exist.
Look at marriage. It is a good tradition but is keeping it only man/woman marriage because that is what is traditional also good? One has to make the distinction between marriage being a good tradition and worth preserving and limiting that good only to one group of people.
Was extending marriage to interracial couples a bad thing because it violated tradition? No, of course not.
Now, denying same sex couples is distinct from interracial marriage because that involved two distinct sexes. But is that distinction in of itself enough of a reason to deny the application of a right to marriage to same sex couples? No, because for something to be wrong/immoral, there must be the question of harm, and only in the most imaginative abstract defense of harm can same sex marriage be opposed.
Is same sex marriage good for the individuals marrying? Yes. Is it good to further stable relationships who are often also raising children? Of course. Those who say same sex marriage is a slippery slope would have to defend why extending marriage to interracial couples wasn't a possible slippery slope itself. Let's judge institutions on their merits, and by its merits marriage of same sex couples meets that test.