not solely, but it is the foundation of the tradition for sure.
this regards to secular and religious marriage and is the reason why the partnership needs to consist of man and woman.
The liklihood of natural procreation under normal circumstances is the cornerstone of marriage.
it has been for centuries so why change it?
People sacrificed animals and other people to their gods for centuries.
People hunted for their own food for centuries.
Men had many wives (by tradition and by force) for centuries.
If we keep marriage (legal marraige) the way it's been for centuries, we might as well revert these back to the way they've been for centuries, too, no?
No.
Humanity evolves over time as culture changes.
Our society is seeing that a person's sexuality has about as much to do with marriage and raising children as the color of corn has to do with the song of the humpback whale.
Children can be raised successfully outside of marriage and can be raised horribly within marriage, so why use that old, trite and obviously flawed way of thinking in any debate?
Insecure people can't understand how people different than themselves can function within society.