You not only have a very closed mind but also little vision.
To start with, he idea of marriage as a sexually exclusive, romantic union between one man and one woman is a relatively recent development. Until two centuries ago, said Harvard historian Nancy Cott, "monogamous households were a tiny, tiny portion" of the world population, found in "just Western Europe and little settlements in North America."
The only reason that marriages between men and women occur is so that they can have children and continue the expansion of the world's population. Nonetheless, that idea is beginning to change given that the world is now overpopulated and many countries are now limiting the amount of children that can be had, if not outright being on the fringe of not allowing new children to be borne.
In many cases, bringing a child into the world is not a "thing of love" but a consequence of copulation (pleasure) and that is not beneficial to the world. On the other side of the coin, true love between two people is a positive to all (not only the couple in love). There is no reason whatsoever for not allowing two people who love each other to get married and make it official, especially considering that bringing children into this world is becoming more of a problem than a benefit. Having two people care for each other will always be a positive.
In addition to all of this mentioned above, there are many countries where polygamy is "the thing! (The ancient Hebrews, for instance, engaged in polygamy — according to the Bible, King Solomon had 700 wives and 300 concubines — and men have taken multiple wives in cultures throughout the world, including China, Africa, and among American Mormons in the 19th century. Polygamy is still common across much of the Muslim world). Polygamy is not about procreation but about pleasuring one person. Do you see that as being right?
I believe that Love is the most important thing that can exist in the world. Love means caring for another with everything one has. Love means working together. Love is contagious as all of us want it but few of us ever get it. To me, being against love between two people is a sin as it means that you are not a person that cares, but a person that ideates life.