OneWithDunamis
Because by definition a marriage is the union between a man and a woman. If they change the definition of this word, what other words will they change next? Communication will break down and everything becomes ambiguous. Look at the Tower of Babel. They couldn't communicate with each other and an entire nation of people was scattered.
Don't be selfish. Think of the greater good of society, if you intend to stay with the society you're familiar with.
1) Lexicon changes over time anyway. I assure you that when you use words such as "Vandals" you surely are not referring to the German tribe that sacked Rome centuries ago.
2) Marriage is a social construct. It can be defined as wished by the Government or the people within a society/community.
3) The Tower of Babel is a Biblical tale and most likely did not occur. If we're talking about the origin of languages, it can be safely assumed that language primarily came about as humans populated the Earth, separated in their own ways, and formed their own version of language in order to communicate rather than some kind of supernatural event in which God cursed everyone to be unable to speak the same language.
4) What advantage is there of having "heterosexual only" marriage? Homosexuals will stay homosexuals and it's not as if they're going to act differently than if they were barred from marriage. Also, it's not as if heterosexuals will lose anything by having homosexuals marry. It's not as if heterosexuals will all of a sudden get homosexually married. Unless they do, in which that's their choice.