The Prime Kirk and Marcus weren't married and had a son.
People will opt to marry/no marry in Trek for the same reasons they do now. The best thing is there won't be any narrow-minded bigots who think they know what love is and who should marry.
For example, I don't see Spock and Uhura marrying, as he'll soon come to his senses and realise what a pain in the neck she is.
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)