Why is this shocking? Most countries will do this. Look at all the former Nazi's who had their citizenship revoked in Canada and the US.
That's why they ask (at least in the US citizenship application) "Have you ever been a member of a terrorist organization?". If you answer "no" and turn out to be one, they say you lied on your application and your citizenship is revoked.
The issue is it broadened it to a political instead of a judicial decision. Your citizenship can be revoked on the basis of a foreign country's conviction (say... Saudi Arabia perhaps?), which didn't used to be the case, and the decision happens from the office of PM.
Prior to C-24 there was a mechanism for stripping citizenship for treason and terrorism, but the bar was higher and at least potentially less political.
That's why they ask (at least in the US citizenship application) "Have you ever been a member of a terrorist organization?". If you answer "no" and turn out to be one, they say you lied on your application and your citizenship is revoked.