The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people. - Ninth Amendment
Gay marriage, abortion and the right to bodily autonomy that underpin them are inalienable rights retained by the people, and states only have authority to regulate those rights with the consent of the people. This is not "left to the states" any more than any other unenumerated right is.And note - gay marriage and abortion have majority support among the American populace, and in many states where they have currently been outlawed.
Calling for a Constitutional Amendment for this is a red herring, as rights do not have to be enumerated in the Constitution to exist. The Constitution doesn't even support the Supreme Court's right of judicial review.