Well, it is incomprehensible to you because you don't want to look at that side and not impartial to it. If you were impartial, you would have seen how media programming is trying to distort the minds of children to believe that it is just a natural phenomenon while you and I know that bad habits can be instilled in a human and they can't regarded as natural because natural things always have positive results unlike bad habits.
About the second part, it is to be noted that Allah (عزّ وجلّ) and Ahlebait (عليه السلام) considered it Haram and threat to human survival both physically and spiritually, you should not really be worried about what other vocal people have to say if you really believe in Ahlebait (عليه السلام). Thus, if they said that it's evil, it must be considered as final words.
Well, for that you should read about the ahadith of Ahlebait more. But, what I know from those ahadith, I will tell you. One of the reason that it's Haram is because Allah (عزّ وجلّ) has created pairs in creation such that each one forms pair with the opposite, thus, declining such a law is actually is saying that Allah (عزّ وجلّ) has mistaken. The Hadith say that the place of the sperm of male is womb of his woman. Thus, anyone who does other than that deliberately has sinned. It is because of that Prophet (PBUHHP) said that commiting homosexuality is kufr. Another reason is that it affects the manhood of a man and womenhood of a female that's what Imam Ali (عليه السلام) said that anyone who alters the manhood of a man will be engulfed with severe punishment. Another reason is that spreading any unlawful thing which is forbidden in Islam, makes a man so wicked that he trangress all the boundaries ending finally into pit of infidelity that is what we learnt from history of all those people who tried to make their own way against the divine will.