That's a purely ethical perspective (although even in that perspective ethics, I don't think your conclusion is clear-cut at all), but Twitter's decision may be based on social damage rather than just ethics. The damage done by someone who represents power when attacking those with less power is greater than the other way around, regardless of the beliefs of the speakers. This, BTW, is why I'm so frustrated when people understand these things to be about someone taking offense. When society approves (or approves by ignoring) marginalizing actions and speech, there is actual damage being done through social signaling regardless of whether anyone present has been personally offended or not.