Once the government had expanded the scope of its powers enough that members of the government, particularly in the courts, felt that they could, by judicial fiat, re-define a fundamental concept of humanity.
Do you really think that the courts in the less intrusive federal government we had in the earlier years of our nation's history would have ever even dreamed of trying to redefine marriage?
It is you that is trying to redefine marriage to nothing, or everything, or whatever anyone wants to make of it.
Conservatives are fighting to preserve marriage.