I don't know what you mean by this. I do know that marriage has changed over and over. It has been different in different countries and in places in the US.
What's one more change? What problem does this creat for you? Doesn't it have some health or stability benefit for society?
Marriage has changed in practice, but not in essence.
It has always been between men and women.
Care to cite another "tradition" so fundamental which has been thrown away?
You can't because marriage is a uniquely fundamental building block to any healthy society. Even the rights to life, liberty, and the pursuit of happiness are not as fundamental to the health of a society as a strong family.
Again, note the history of the blacks in America. If you didn't read that post, let me know and I'll repeat it.
Shalom.