Personally, I think it's not really a "gay" issue. It has more to do with the need to of some people to try to put everyone in boxes & insist they stay there. Most people see the world as black/white, male/female, digital/analog etc. Many people get unhappy, upset or frightened, when confronted with a reality that is more complex than that.
For the moment, let me put aside the issue of homosexuality. Let me pose a question of Biology.
What is a Man? For the moment, let's say folks who are XY = Man/Male
What is a Woman? For the moment, let's say it's folks who are XX = Woman/Female.
What about folks that are born Intersexed? Someone who on a cellular level is not completely male or female. Some intersexed folks might have chromosomes such as: XXY, XO, XXX or even XXY/XY Mosaic.
Intersexed persons occur in 1% - 4% of the population.. about the same rate as Redheads. Most folks who are intersexed, don't realize it. Many of them appear & believe they are 100% male (XY) or 100% female (XX).
With whom should that person love & have the right to build a life-long partnership? Suddenly it gets all complicated. After all, if a person's chromosomes are say XXY or XO or something else, what would be their opposite gender?
And they live their lives, fall in love, and sometimes marry. If we define marriage as something that can only legally occur between men (XY) and women (XX), we have made their love illegal... because of their biology.
Please tell, what would the moral basis for this be?
And the difference from heterosexuals is?
Personally, I think it's not really a "homosexual" issue. It has more to do with the need of some people to try to put everyone in boxes, and insist they stay there.