Nature is not a steady methodical operation; there are errors and mutations that occur that can be inexplicable, creating many problems. The greatest drive in all nature is the preservation of the species; however, homosexuality does exist, which it has from time immemorial. This is biologically mystifying, however controlled through natural selection, a Darwinian process that assures the continuation of the species.
As to the political aspect of this problem, those in Philadelphia in 1787 stated quite clearly that the new government was established to ensure that everyone would be granted life, liberty and the pursuit of happiness. It must be said that they did not take into consideration Indians, blacks and women at this time. The few that have been caught up in this biological sexual twist should not be denied their relationships, as long as this desire does not harm others, which it doesnt except in the warped minds of a few.
The term marriage and all that it pertains is a part of this problem, and because of the turns and twists of social history, it has achieved a certain predominance , which should not alter the initial idea of the pursuit of happiness.