No it's more to do with fairness to all, not just some.
And it is this idea of what is fair and what is not, that is at the root of the issue.
What "long term consequences?"
I have neither the time nor the inclination to spend a great deal of time on explaining it to you if you do not already know my well documented views on the subject. To do so would be a massive waste of time. In my experience, people who've made up their minds on this issue, will not change them. Suffice it to say that my argument stems mostly from a breakdown in the family over the last 40 years as leading to the direct result of why our country is as screwed up as it is. Gay marriage would add to that breakdown, it would not solve it, or improve it in any way. Kids need both their mothers and their fathers active in their lives and as direct role models. Uncles and Aunts, and neighbors, or schools do not provide for these needs, and until we decide collectively as a nation to restore these virtues, we're destined to fall even further as a once strong familial based society.
Laws are representative of a societies values on justice and punishment. Libertarians, as I explained, just want to be in the drivers seat, as do conservatives and liberals.Nothing wrong with freedom ... fascist.