The avatar is something he spent time on and valued. He was cheating in order to take things that others had spent time on and valued. So killing his avatar as

The avatar is something he spent time on and valued. He was cheating in order to take things that others had spent time on and valued. So killing his avatar as a response to these "crimes" is equivalent to taking someones property or money as punishment for theft. I'd hope you'd agree there are moral questions about what constitutes a just and proportional response.