I wouldn't call this a broad definition of mental illness.
Even better then, but I wanted to be sure people understood I wasn't giving a clinical definition they could nitpick about from what they read in their psychology class.
I think it's reasonable to suspect that the person who does such kind of attack, knowing that he most likely will be killed after that, has at least some kind of mental health issue.
I think this is too broadly defining mental illness. People die all the time for a cause, especially when it is perceived to be a war for the soul of their society. We have evidence he shared these beliefs. I don't think people like this are mentally unsound unless their families confirm they had problems perceiving reality, even if I disagree with their reasoning.