Well, the slightest suggestion of Vulcan tampering with human genes (to wit, a Vulcan-human child) was considered abhorrent in the 2150s still. If most people had Vulcan genetic engineering to thank for the fact that their great-grandparents survived to have viable offspring, it would probably be more difficult for Terra Prime to fan up the racist indignation.
Vulcans might have done a lot covertly, of course. Might tie in to that merging of Star Trek and Larry Niven's Known Space in TAS "The Slaver Weapon": Vulcans are Star Trek's Puppeteers, secretly manipulating mankind and other species for greater utility in their schemes of world domination. Or at least of making the universe a safer place for Vulcans, with the manipulated humans now volunteering in droves to defend Vulcan via Starfleet.
Wouldn't the greatest significance come from those who judge, rather than from those who do? The same deed (say, carpet-bombing) can be good or evil, depending on whom you ask.
Or then it is.
But what suggestion is there that these health issues would be more prevalent? Previously, people just died in horrible ways before they had time to worry about allergies.
And as pointed out above, lactose intolerance is one of those things that the modern world has made virtually disappear. It used to be a global problem before we invented "global". Now we travel, and fuck strangers from afar, and soon enough everybody can drink milk.
How is that different from the past where, at various times, the kids have been raised by grandparents, strangers or nobody at all, because there did not yet exist anything one could call free time?
Weren't you worried about "less real interaction" just a sentence before, though?
Timo Saloniemi