are there any studies that show exposure to genitalia
during childhood leads to psychological damage of any kind
No, none at all. If that were so, many generations before us, and most European generations, would be quite damaged. The epidemiological evidence speaks for itself.
and that this social taboo is, to some degree, absurd
Completely absurd, period. It's confusing genitalia with sexual activity, completely disregarding context.
There are some studies done in Denmark in the seventies, where small children were shown danish soft-porn movies, and a control group were shown 'Bambi'
If I remember correctly, the kids where not reacting in any special way to the porn, and thought it was nonsensical or plain boring, except the humorous segments (think Benny Hill but naked, typical of danish pornography of that era) which they laughed at.
However, a large percentage of the kids in the control group reported nightmares from Bambi, and many children reacted badly to the death of Bambi's mother and other dramatic events, and it occupied their mind for a long time after they watched the movie.
Edit: On the other hand, 95% of the internet porn of today is probably not good for anyone to watch, and especially young people seems to have a rather bent view of sexuality and especially women's sexuality. But seeing naked people, can't possibly be damaging for anyone.
