When society decides there is no longer any need for state recognition and/or regulation of marriage, then there will no longer be state recognition and/or regulation of marriage.<quoted text>
.....nor number of participants, pre existing relationship, etc. At what point is there no point and thus no need for state recognition and/or regulation.
The mere recognition of marriage is discriminatory......certainly against single people.
Again, it's up to society to decide.
Nope, single people aren't banned from getting married just because they're single. And if they do choose to marry, their marriage isn't treated any differently than any other marriage just because they were single. Therefor marriage laws giving specific rights/benefits to married couples but not to single people meets the constitutional standards of equal protection.