I don't like this contrived example though, and I suspect you've only set it up so that if/when I say "nope, I won't sell the gun to that person" you'll then say "in this case the gun is GitHub and the felon trying to buy it is ICE" which I do not think is an apt analogy at all.
And would you have the same answer if you believed that law enforcement wouldn't do anything to stop the buyer from doing anything?