The manner in which it's mocked may disproportionately impact some groups. If (for example) minorities have higher levels of imposter syndrome, that sort of "you're an idiot" mockery might knock disproportionate numbers of minorities out of the field early on.

I think you are right that minority status rarely has to do with the mocking, but I also think this might be beside the point. I think really the concern is that people who might already feel like outsiders are easily discouraged and made to feel even more like an outsider. And as it turns out, it isn't even hard to identify as an outsider on stackoverflow, even if you are a great coder! I just checked out the stack overflow public survey for 2018 [https://insights.stackoverflow.com/survey/2018] - 92% of users are male, and 74.2% is white or European decent. Seems significantly homogeneous.

Homogeneous if and only if you consider "white or European" to be a clear cultural classifier. Personally, I think that there are massive cultural differences between the US, Canada, UK, Australia, and every country in Europe.

As an Australian, I'm a global minority and it might shock you but don't identify with many US cultural groups who are the overwhelming majority online.

Your point is what? Who cares if women or minorities feel unwelcome, they haven't walked a mile in your aussie shoes? Dude...