Irrelevant. Plenty of U.S. born persons have been injured in construction accidents.
What happened is his responsibility alone.
No, it simply is not, no matter how many time you want to say it. He and the subcontractor had an agreement - he worked, and in turn, was compensated. I highly doubt part of their agreement was "If you get hurt, tough luck". Aperson does not lose natural and human rights because they are in some geographic area "illegally". He still has the right not to be injured through the negligence of another. This isn't like some thug breaking into your house, cutting himself on your broken window, and demanding you compensate him. Not even close. The sub-contractor is 100% reposnisible for the injuries, unless the injured caused it himself(which isn't alleged in the story). His "legal" statuse does not remove liability from a negligent party.
Come here illegally and get hurt, tough. Cry to mother mexico.
That's a warped sense of repsonsibility you have there. So, are you telling me, that if I find a Mexican who just crossed the border, I have the legal right under the laws of this country, and the moral right, to beat him, rob him, rape him and enslave him? I mean, that is essentially what you are saying - the person has no rights and its "tough". Please clarify if that is not your belief.