Perhaps restricting the analogy to nuclear weapons would make sense. Only nation states (software companies) and terrorists (malicious hackers... and perhaps intelligence agencies) would be interested in purchasing such weapons.
My thought is: if one argument is good and another is bad, clearly the reason for the difference does not exist within the properties they share. It must exist where the arguments are different, or more likely in this case (as what the poster said and what I said are so similar), in the outside world of facts and understanding.
But if the shape of the argument allows for things that may successfully convince you, then clearly that information is not enough to dismiss it outright. It should be the start of a dialog with the parent comment.
Now, for something completely different:
If, for some reason, you want to actually engage _me_ on this particular policy issue, angle your thought at this: my understanding is that it's 2014, and if you want to regulate the information people share or sell over the internet you've accepted a challenge I do not envy.
I would be particularly skeptical you could do this without building a comprehensive computer spying system and perhaps outlawing crypto (it's been tried), as you're trying to read communications of highly security-conscious people.
As for if Mitnick is a good person (or similar things under discussion here), I have not met him.
Replacing "vulnerabilities" with "firearms" while retaining the same argument structure does not mean that both arguments are logically identical (a false equivalency). The implications of a free market for information security and a free market for firearms are totally different.
If you cared a lot about Internet Points, I'm betting keeping a sockpuppet acccount just to post "why was [master]'s post downvoted?" comments would be one of the highest-ROI things you could do to get more of them.
I should also note that I've seen a lot of early-greyed posts come back from the dead after 30 minutes or so even without the "omgwtfisgoingon" posts underneath them as well. Sometimes even becoming clear winners on their strata of the post's comments.
You prompt a fascinating hypothetical: suppose all the world's atomic weapons were put up in a free, transparent auction? (i.e. bidders and bids are disclosed)
I'd argue that most would end up in the hands of good actors (e.g. the world bands behind the Dalai Lama to buy and destroy them all), but who knows? Good debate topic for happy hour, though.
Imagine he had said: I believe a free and open market for weapons would be a good thing, because it would reduce the number of defenseless people, would result in a power imbalance that puts generally-okay actors at an advantage (say what you will, but the mob doesn't have 1% of the resources the US government does), and would therefore reduce crime.
I do not personally find that argument compelling (and it is of identical structure to the above), but me disagreeing with it does not mean it isn't of sufficient quality for Hacker News.