To be sure, the big argument against this being Spock's wedding is that Picard later meets Spock in person, and there is no recognition of this earlier meeting. That is, Picard says he has met Spock once, but the issue of this meeting, or the marriage, never comes up when they meet the second time, in "Unification".
Sure, Picard would have been a self-acknowledged "lowly lieutenant", and Spock a busy celebrity. But Picard wouldn't forget this momentous meeting - and Spock simply doesn't forget, period. And what better time to bring up the issue of Spock's marriage than an argument about Spock's duties to the Federation? Picard would have the perfect chance to remind Spock that his wife is waiting for him, worried (in a logical manner, of course).
In "Sarek", Picard has met Sarek once before, in his son's wedding. In "Unification", Picard has met Sarek's son Spock once before, in unknown circumstances. It's a possible match, yes. But it doesn't mean the two sons would be one and the same.
I'd personally much rather have the private evil of individuals taking advantage of the disabled (and usually this is a very arguable, very fact-specific inquiry) than the public evil of a state regulating by law, or a society regulating by approbrium, the sexuality of human beings who have passed the bright line that age of consent laws provide.
The difference between this, and an argument on sex with children, is relatively slight. In both cases, it can be argued that sex (just like other acts of forcing nature, such as physical punishment, or opening the TV, or giving vaccinations, or feeding raw carrots) can be detrimental to the future development of the victimized individual, but this is difficult to demonstrate unless a time machine is humming on the driveway. Also in both cases, definite perpetrator and victim identities are easily assigned, based on the mental and physical states of readiness and their role in initiating and controlling the practice - unlike in the case of, say, homosexuality or marriage or competitive combat sports or other controversial practices.
Would there be a defining difference there? To what degree should sex, or TV, or vaccinations, or carrots, be consent-based, to what degree should they be regulated, and to what degree should they be a private matter?
The close resemblance between the practices is probably the real reason for the taboo about sex with the disabled. It's simply rooted in the deep-rooted taboo about sex with kids and other parties that cannot give informed consent. And it sidesteps the issue that "informed consent" is usually unattainable in almost anything, because people aren't really "informed" about anything unless they try it out for themselves...
Timo Saloniemi