The military switched from larger caliber bullets (30-06) to smaller caliber (.223) because they found larger caliber bullets tend to kill the intended recipient. That would take one soldier off the field. However, if you wounded one, it would potentially take three - the wounded soldier and two more soldiers to remove him from the field and save his life (and I swear to god, if any of you people come in and anal-rententively correct me on a technicality I'll murder your cats).
The same tactic is being employed here. The enemies of western civilization are not so much concerned about killing targets one at a time as much as they are resource consumption. THis scum bucket has consumed, in terms of time, more than just one Brit's life and thus caused more damage.
Of course, if Britons wanted to grow a spine and just start throwing/killing scum like him out, they could. But that wouldn't be polite and the lefties would scream bloody murder. Plus it would require self-respect and an appreciation for western civilization.