Why not just call girls boys?
Marraige is a union between a man and one or more women.
If you 'marry' a horse with an as s the result is a donkey. Why would anyone try and call it a horse?
If you want to join two or more of the same things, it is simply more of that same thing and not a marraige.
You can marry two dissimilar ideas to create a new idea. This is marraige.
Rice plus rice is still rice. This is Not marraige.
Bastardizing the meaning of a word is not necessary to accommodate unions or joinings of similar things even if you are pro homosexual.
There is no such thing as a marraige of two identical things. A new or different word should be used, but I don't want the meaning of the word marraige to be unnecessarily changed.