I believe that individual liberty demands that consenting adults be allowed to arrange their lives as they see fit, as long as it doesn't interfere with the rights of others. Part of that arrangement would include making contracts with each other -- which is basically what marriage is in a legal sense (as opposed to a religious or personal sense, which the government has and should not have any control over).
We are free to praise or condemn, as we see fit. But the government should not be permitted to prevent consenting adults from arranging their life.