WHat is being fixed is eliminating the discrimination and infringement of individual equal/civil rights
2.) no it factually does not because states have no right to infringe on this
3.) no door is being opened, this strawman always fails, the slippery slope argument. Same argument with womens rights and minority rights and interracial marriage etc.
if we consider blacks to be men/person we might as well consider my dogs to be people too, where does it end
if we let women vote we might as well let my horse vote, where does it end
these arguments were illogical and they failed back then and the same remains true today
"others" can want modification all they want unless they can make a case for equal/civil rights they have nothing to work with, theres no legal precedence about illegal discrimination, rights infringment and equal/civil rights about hetero/homosexual marriage that lends usage to others.