In Spain, homosexual marriage was legalized in 2005 after the Netherlands and Belgium. It was an extraordinary step forward for society in the field of culture and human rights. But even today, we are still homophobic, and we do not accept this marital bond at all. 

By my part, I think that all people have to be happy, and this implies being free and equal before the law. Laws should be for everyone, and sexual orientation should not matter. If we talk about the issue of having children, it is not necessary that they are a man and a woman. 

On the one hand, we have adoption of children, and on the other hand, we have assisted reproduction (in the case of women). That's why no one can make the excuse of the children to defend themselves. Marriage is civil and not something religious. Each religion then evaluates whether it accepts it or not.

Finally, I want to say that there have been older people (from ancient times) that have accepted this, so that's why, with more reason, we should do it. We all must be happy whatever we are and however we think. Remember that you only live once, but if you do it right, once is enough, so be happy and let the others also be.