I think there is a very big difference in perspective here.
The only one who is allowed to grab a woman in a playful or affectionate way is her lover. No one else is allowed to do so, ever, for any reason. Being female and having breasts does not give the males of the world permission to do as they will, when ever they feel like it.
Harlan's actions did not spring "from an unexamined sexist part of himself." A man, any man, who sees nothing wrong with assaulting a woman like this does not view women as fully human. They see women as property to be used as they see fit. There is no respect for women as unique individuals in a act like this.
Assault like this is all about power and control. It is all about asserting dominance. It is no more about being playful and affectionate than rape is about sex.
This is not an isolated action on Harlan's part. It wasn't even the first time he'd touched a woman in a way she objected to during this con. It was just the most public instance.
And frankly, attempts to excuse his behavior make me slightly ill. I'd hoped the days of women being viewed as playthings and so much meat were long over.