I get being afraid of the strong summoner. But if they were smart, they wouldn't try to antagonize him. They needed him to win against the demon lord, if the Mc was more vengeful, then they would've been dead.
And what happens if his summons are released right there when he dies? Now there's a bunch of monsters without a master in the middle of a crowd of civilians.
They should've just tried to send him back.
In the end, he was just some guy they decided to draft. It's like kidnapping a soldier from another country and telling him to fight for you.