I really like how this implies that all boys are sex-obsessed monsters that would rape without a second thought. Except I really don't like it at all.
I agree with you and feel the same way but I'll play devils advocate here. Normally guys get eased into the flood of hormones and if they have proper support structures around them they've been taught how to handle it and had it drilled into them to control themselves from harming others. Even then most boys jerk off daily or multiple times a day. I can't imagine never having these urges or thoughts and then one day having to deal with the flood of all of it at it's peak. Honestly I'm impressed she held out this long. They really should have told her to jerk off instead of sticking a cold pack on it though if its that bad.
You could also argue it's implying because she's a girl she doesn't have the same willpower as a guy and if women had to deal with the strength of instinct guys do that they wouldn't be able to handle it. She seemingly even goes for her own sibling which instinctually is a huge no no. She lasted less than three days and that's with the older sister reverting her back for periods of time. She's also the first person we've seen try to assault anyone. The only other characters are the mad scientist who doesn't care about consent to medical experimentation and a yandere who chased off other girls in order to keep the dude isolated to herself.
At the end of the day its a dumb manga where a dude turns into a cute girl and a chick gets a Ron Jeremy sized endowment. I don't think you should always ascribe what personal beliefs a mangaka has for situations they put in their stories for "plot" reasons. Except that the author likes dick girls.