I can actually accept that THAT was the reason why the MC was cursed. I can understand why some would call bullshit on it, though.
From what I've seen, they went through a great deal of pressure and frustrations. Years upon years of mindless violence, doesn't do well to your psyche. You get desperate, and twisted.
But on the other hand, it's not very fulfilling of a reason. I feel like it would've been better to start off from there, rather than try to use it as a mysterious plot-point -- the MC would know why he got cursed, and be told to "lie down already and learn your lesson", but fail to notice that the curse was too strong and nearly killed him, and then he'd break the curse by essentially doing what they wanted to prevent him from doing: playing the self-sacrificing hero. Essentially, irony all around 24/7.
As-is, the MC being cursed to die, as the story started, and the reason why he got cursed being played "as a mystery", can easily makes this chapter feel stupid, yeah. This story should get a re-write, tbh.
EDIT: After reading the comments properly, I agree that this whole development is really dumb. But, I also feel like this sort of plot *can* be played out if it was written in the proper sequence.