Natural selection doesn't really apply to human's anymore... we support even the most disadvantaged people enough so that they can procreate.
Your argument concerning the "out of Africa" theory is imo correct; but doesn't have anything to do with what Camail said.
Sure, back when it was difficult to survive, those who could produce more Vitamin D with less sun would be more successful at procreating.
Now, as you said; we have AC, vitamin pills, houses, etc.
No matter what kind of pigmentation you have, you have equal opportunity to reproduce.
You seem to be confusing Darwin's theory with Lamarck's.
Things don't evolve just because it is advantageous to the species, it HAS to be because it provides a better shot at reproduction.
In this day and age, nothing stops us. Thusly, we never evolve in any particular direction.