To my eyes the ethical question is, Do I think that this system, written in Perl, will be an improvement? If it is, then I'm willing to go ahead with it, and I'm willing to accept responsibility for potentially killing people. (I would, of course, be extremely cautious, insist on code reviews, pay a lot of attention to testing, etc, etc, etc. I'd also be very cautious about quality control with external modules, etc. If you're working somewhere that deals with these kinds of issues, they undoubtably have procedures. Take them seriously and follow them.)

Then again I'm married to a doctor. That does change one's perspective. You learn that people are killed all of the time by accident. But don't let that paralyze you because people also die because of hesitation. And sometimes you simply have to gamble with someone's life. If you're unable to live with that, there are some jobs you should not have.

Oh, and I've also heard enough horror stories that I'm more willing to accept imperfection. That's why I cited improvement as an ethical standard. If you kill 50 people because of a bug, but you've saved 150 because the new system works better than the old, then you're up 100 lives. It would be better to be up 150, but 100 lives saved is nothing to sneeze at.