It's the perspective of the ousted Drupal member that his beliefs are entirely packaged up in the BDSM subculture that he takes part in, and that to have a problem with his beliefs is to persecute his BDSM subculture.
It's the perspective of the other Drupal members who ousted him that his beliefs are not in fact cabined in that subculture, but in fact bleed out of it into his interactions with the broader world. They cite evidence.
Since the beliefs that we're talking about could be broadly and probably inaccurately but by how much I don't know described as "females are subhuman", it's the perspective of the Drupal members who did the ousting that those beliefs matter very much to the project.
I don't know what the right answer is, but I do know that this TechCrunch article basically defined away the controversy. That doesn't help anyone make sense of it. I'm happy letting the Drupal community work this stuff out for themselves though, and also flagged this story, which is, after all, really just drama.