There's a slash panel at CONvergence every year, and aside the year when one of the panelists showed up drunk (it's held at 11pm, as many of the 'adult' panels are in the evenings after children go to bed) it's not been hugely problematic. The idea itself isn't bad.

It's also not pitched like that. But then again tumblr gets super angry on a moment's notice if they think something is being exclusionary or bigoted so a tumblr convention should have known better than this.