It's not just about one incidence of some mistakenly pedantic comments, as has been made clear by many, many people. It's a pattern of behaviour over years combined with no interest in listening to other people or accepting that he might be in the wrong. His behaviour towards women in particular has resulted in a lot of people sharing stories of his behaviour which, on their own, should be enough for someone to be considered a problem. This latest incident is just what it took to finally tip things over the edge.
This article then goes on to talk about people like Stallman being needed, or essential for something like free software. It doesn't matter, even if it was true, which there is no way of proving, it's pure assertion. Phrases like "required someone who couldn’t take a hint" might sound all perseverance and dedication to this writer, but perhaps going and asking women what comes to mind when they hear about people like this might be an eye opener.
Without him students wouldn't have as many free tools? Maybe, but maybe they would have other tools, better tools, built by the people his behaviour, and the behaviour of people like him, have driven from the industry before they got a chance to have the impact that people like him seem to assume is a right.