I can't speak for cft, but there are two glaringly obvious reasons. One cultural, and one of a variety that cft is absolutely correct about:

You will be downvoted, flagged, and then dang will arrive to warn you that this specific argument is not permitted on HN because it inevitably leads to unproductive flamewars.

To be fair, dang is completely correct in this observation. It never leads to productive discussion, but it is nonetheless verboten.