I personally think you were right to lash out. The GP was spouting hateful anti-male crap which will influence the young developing minds s/he's teaching to think that men can never be good and civil, and all girls are angels who only fall if men cause them to.
It's telling the boys that they can't escape the baseness of their gender, and it's telling girls to never trust a boy (but always blame them!) It's a skewed view of life, it's fucking up children, and it's exactly what the catholic church did to me (I'm not bitter at all).
Sure, biology plays a part, and men tend to be more casual about sex and girls more picky (some will disagree). But
... and being able to post it in a searchable form on the internet are all very different things.
They didn't post it! People keep saying what they did is wrong because of X, when they never did X. Sheesh.
"Ninety percent of baseball is half mental." -- Yogi Berra