I am opposed to any form of corporal punishment for children, but I think that using tickling as a punishment would be especially horrendous. The vast majority of people will never become tickling fetishists, but even vanilla people use tickling throughout their lives for all sorts of purposes, including flirting, intimacy, playful roughhousing, etc. Tickling a child as a form of punishment will pretty much guarantee that the individual being punished will grow up to view tickling as something negative, thus preventing him or her from having any positive experiences with tickling as life goes on.