Not disagreeing about the cruel part but some of these birds live and breed because of humans. They survive in place where they couldn't without humans.
For a bird to get caught usually implies they aren't feeling so good.. imagining killing a sick seagull makes me sad.
They're aggressive and rude about trying to survive, yes, but we're top of the food chain, and have kinda nicked a tremendous amount of their fish out of the water.
(Shrug) what's done is done, but I'd lose a lot of respect for this man if I knew him.
I've caught one before as an early teen for a bet. It wasn't sick to my knowledge, just utterly unafraid of people and no harder to wrangle than a chicken once you get in range.
My memery aside, I agree bare handed killing a seagull to take revenge is sorta barbaric, which is why this isn't actually a pro-brit meme