Enabling their hypocracy? It isn't exactly unfair to call out this kind of joking when a cornerstone of men's issues is that they often aren't taken seriously when things like mental health issues arise. They're often dismissed with jokes or belittled.
In other words, the person who came in joking failed to read the room and got called out for it. Would you defend someone saying, even facetiously 'bet she's just saying that for attention ' in a rape support thread?