Sure "Anonymous" has mostly remained nonviolent, but they regularly harm innocent people to attempt to acheive their goals.
"Political violence against civilians" isn't quite right, because "civilians" can nevertheless wage war. What happens when two nations fight against each other with the full backing of their "civilian" populations, who actively provide all of the funding and materiel to fight the war? Is it off-limits to attack civilians? Should that sort of warfare be lumped in with terrorism?
Unprovoked, unilateral attacks seem to be the more traditional form of terrorism (basically using fear to try and influence behavior), in particular when performed by groups not (officially) affiliated with a specific government.
I can understand being apprehensive about violence against non-combatants, but in the above situation what exactly is the justification for excluding attacking civilians?
So on the efficacy front, it didn't make sense, and on the honor front it's on some pretty shaky ground. Of course, it happened, so there's that.
But even hamburg was a major center for the support of U boats so you can see why the threat of the later Elektroboote Tpe XXI boats would put them on the target list.
Oh and my Fathers house was hit by a bomb - but they where going for the Largest Spitfire factory in the UK so it wasn't his house they were trying to hit.