I am sure it was “difficult” to repeal the Jim Crow laws, but difficulty to implement does not affect whether something is just.
The fact of the matter is. Polygamy was the norm through most of human history. Gay marriage has never happened.
If gay marriage is legalized heterosexual marriage will end. Marriage will simply be a contract of shared property between any 2 (or more) people living together. The institution will cease to exist in legal form.