I think "difficult" is a tough term to pin down. I was troubled by the fact that the assumption was made as if it was a scientific fact; especially since making the assumption clearly eliminates a valid answer to the question.
Maybe I just took too many logical reasoning / philosophy classes in college...
Meta-discussion remark: whenever I point a flaw in an argument I try to add a disclaimer stating that I'm not necessarily taking the opposite side. This seems to cool down the discussion a bit, especially if the argument in question is in line with the HN (hive-)mindset.
Edit: This was meant as a response to your comment about being downvoted, sorry.
Maybe I just took too many logical reasoning / philosophy classes in college...