a marriage is a marriage as long as it is between two consenting adults of the opposite sex. a gay marriage is not a marriage. the same examples (as the ones you mentioned) cannot be used for it is not the same thing.
for one thing, a gay marriage does not procreate. and whether you like it or not that is part of a natural marriage. it is not ALL about sex ofc, but that is part of it. so stop saying, oh you think of sex only. no i don;t but that is one of the functions of a marriage that cannot be replaced by your so called 'marriages' of gay people