A Constitutional Amendment is put into effect because if affects everyone.

An amendment banning gay marriages does not affect everyone. It affects gays. And gays only. All the people bitching about it ruining the traditional family would not wake up one day and feel worse if two gay people got married down the street. Their life has not been affected in any way. If they believe the opposite they are retarded and should be put down.

The same reason is why there will never be an amendment banning abortion. It does not affect everyone. It can be threatened and brought up time and time again, but it just won't happen. Any issue so controversial will always have a large enough group opposing it that it will not matter who is in power. Politicians do not piss off half their constituency.