"Becephalus, when you read several responses from different readers here, to different letters, and you find the responses generally crazy, there's only one consistent factor there. You."

Bingo!

The consensus seems to be pretty much that the tickler is at best a dick that doesn't respect her enough to listen to her pleas to stop, at worst he's in the beginning stages of real abuse.

My theory is that the guys who are excusing this behavior have done it themselves to a girl in the past, and really really want to think that 'it's just tickling, no big deal'. They don't want to believe that it is showing true disrespect to another person's boundaries to continue repeatedly once someone says Stop!