I don't think defederation is ever justified outside of technical reasons, like spam or other disruptive activities.
I don't think killing civilians is cool. (Each side feel free to project your biases onto that comment)
I think that there is a large population of people who share the toxic view that social media is a battleground and views people who disagree as enemies to be attacked. These people are often disruptive, toxic assholes. The way to deal with them is to ban them when they pop up.
I think it is extra stupid to stereotype people based on the instance that they signed up for instead of their stated opinions.