That's an appeal to authority and an attempt to shut down inquisitive thought and investigation.

Imo, this goes against the spirit of HN.

A better response might have been to point out that the level of POW is reactive. If there are no attacks ongoing it will use little to no resources. If it's effective, the attacks will largely stop (no point in attempting an attack that won't work) and so paradoxically this can potentially provide its benefit without actually having much usage.

If it works out that way the benefit vs costs are very good for pretty much any way of evaluating the costs. This is the kind of nuanced thinking that you'd expect from smart people, as the prior poster suggested (and, in fact, is pointed out in the design document).