It's not stupidity, and calling it that isn't just facile, but detracts from the larger issue.

The problem here is ignorance, and warped values. It's not that these people have sat down with all the relevant information, been told all sides of the story, etc and said "yup, you know what, after being shown the facts and thinking about it, I've decided that forcing someone to have sex isn't the same as rape". Instead, the problem is that (and I'm speculating here since the study didn't measure this) the general perception of "rape" is something that happens violently in a dark alley with a guy in a trenchcoat -- not just any non-consensual sex.

The distinction is important, because if you just treat these people like they're stupid, then you'll never actually change anything. You need to instead treat them like they're ignorant, and start educating them. I don't just mean boring public service announcements or educational posters. I'm talking about actually sitting down with kids and engaging with them, having discussions, talking about their perceptions and experiences and offering a broader, more representative perspective on the issues.

It needs to be a dialogue where people can ask questions and argue and debate and seek clarification. It needs to be one where people can share stories and help highlight the issue from different points of view. And that includes the point of view of guys who are baffled by the fact that if someone consents while intoxicated it's still rape. That is a really fucking hard thing to wrap your head around and if you treat people who don't instantly accept it at face value as stupid then you just distance them from any sort of engagement with or acceptance of the issue.

This is not a 'common sense' problem, and education here requires a complex and nuanced approach, and one which is open to the sorts of discussion and inquiries and concerns that young men are going to have with what they're being told. That's the only way it's going to work.