No man has a right to marry anyone...
A valid right is that which where such is exercised that such does not usurp the rights of another.
Where such undermines the viability of the culture, such is rendered morally unjustifiable and as such is not a right of any kind.
Its not a complex issue sis... its just one which falls beyond your means to comprehend.
However, you have to prove that the viability of the culture is undermined...and you have not done that.
Nope... that's established bydefault, through the natural tendency of the species to dry right up where homosexuality catches on... add to that the promotion of debauchery, hedonism and general degeneracy... as a rule... those things are not the things which sustain a viable culture.
Marriage and sexual activity are mutually exclusive...
There is nothing preventing a man, who is married to another man, from reproducing with a woman.
In addition, you are mixing up the concept of species with culture. If you were concerned with a species "drying up", you would not allow heterosexual marriages where the couple decides to not have children.
In fact, if you wanted the species to proliferate, you would not allow monogamy.