YANBU. I see no one here who thinks this guy was "just doing his job" has addressed the point on Bloody Sunday.
If we allow the army to go round being judge, jury and executioner and gunning down unarmed civilians on the streets then innocent people will be shot dead.
It doesn't matter if the victim was guilty as hell. It's the principle - this was on the streets in the UK.
And how do we know innocent people will get shot too? Well beside the very real risk of mistaken identity, and of the falsely accused being shot (e.g. the Guildford Four - what would this gunman have done with them?) there's also the culture it built which led to soldiers taking it upon themselves to gun down innocent civilians on Bloody Sunday.
Please think about this, if you're saying it's OK for them too shoot a known IRA member then you're also saying you condone innocent people to be shot down on UK streets, because that's this kind of murderous action has been proven to lead to.