Lol maybe you shouldn't be summoning a bunch of people from another world to begin with then blame them for everything lol. That first chapter was just a bunch of ass backwards logic.
The summoning itself was already illegal, though, so the summoners are held responsible as well. And based on the title of "Stray" given to the otherworlders, it seems like they can sometimes just end up there even without it , simply because of Truck-kun. In any case, their overwhelming power is (believed to be) a danger to the world itself, so it's not that ass backwards to eliminate them ASAP based on the (so far generally accepted) facts.
I mean they rip him out of his world, cast him on the streets as worthless to basically die on his own. I think I'd be pretty hell bent on fucking up some people too. It's not like he said he was going to go massacre people willy nilly. The icing on the cake was this all being a ploy to use him as a decoy in the first place, though he wasn't aware of that.
They deserve some payback.
Not saying they don't, and they likely will (and some already did in the second chapter).