@denis - ahh, the self-righteousness of youth.
When arguing with your elders, you should probably research your statements and find out if your statements of fact are, essentially, fact-based.
"A. Marriage is a bond between a man and a woman, and that belief has been upheld through society for thousands of years"
Bzzz! Sorry, one strike. Marriage has changed over and over again over thousands of years. Polygamy has been VERY common through the millenia. Did you watch the movie 300? Do you know WHY the (real-life) 300 warriors that slowed the invasion were so loyal and willing to stand together? Because they were pair-bonded, and they loved each other. No, the movie didn't make that obvious. But that's what actually happened.
"B. Men are not supposed to have sex with men. Because it's immposible and even if it was possible the point of sex isn't there as men can't birth. So I don't think nature would allow men to be born gay."
You're not talking about love, or marriage, or even sex. You're talking about reproduction. If you haven't noticed, reproduction doesn't require marriage, just as marriage doesn't require reproduction. Would you make it illegal for a man to marry an infertile woman? I have some families full of adopted children I'd like you to meet. Is it illegal for a man to have a vasectomy and be married? Have you noticed a number of children being born out of wedlock?
Some day some nice girl is going to offer you some kind of sexual activity that doesn't involve intercourse - or even uses contraception. By your logic, you would turn it down, because sex for any reason other than reproduction is "immposible".
You've already told the forum that your parents are very rigid and have strong religious beliefs which you don't share. If you truly want to think for yourself, you probably should take some time to explore the world around you before declaring strong opinions. OTOH, it's much easier to simply parrot the teachings of the intolerant.