Life Critical

What is a life critical system? I think about this all the time. Some might say that a life critical system is one that is critical to sustaining life. Others have said that a failure to such system may result in death or serious injury. And even others have said that there is no such system. I tend to drift towards the first group of thought, however this uncomfortably opens up debate around some systems and their true value. What I mean by this is to question if there are systems out there that threaten the sustenance of life? And more importantly, if there are such systems, what are we going to do about them. Many smart people have put much thought and careers into this question. The problem is that the other people only see the money required to design and build such systems so that that life is not threatened. My take is that the business case should include the cost to maintain life, if in question. However, on the opposite side many technical evolutions would not have occurred if we did not take these risks. But, what is more important and what would have happened if these risky evolutions did not occur?

Tell me your thoughts?