Government needs to keep enforcing that definition, or else it doesn't exist, the Mormon Gods would still have Polygamy, Allah would still have polygamy, homosexual churches would have always had marriage.
Letting marriage be defined by any and all, no matter how bizarre or far afield, means that what we have always thought of as marriage, just no longer exists.
Oh?
I don't care HOW many folks say my blood is GREEN - it is STILL going to be RED!