> "I think it’s impractical and unaffordable because A: anyone who wants to (and has enough money) can write to your “secured” database (lol) and B: even authorized users cannot reuse the PoW."
I was referring to PoW in general, not Bitcoin's specifically. Of course PoW would not be the only security mechanism in place, just one of the pieces. Consider the Hashcash idea of using PoW to fight spam; an email with dedicated PoW attached has a lower likelihood of being spam because sending out large volumes of such messages would be very costly. Perhaps similar ideas can be applied to prevent some types of DDOS attacks.
> "So if there are no control values that make sense to put behind PoW, then the “pissing contest” argument doesn’t make sense to me either, because having nukes is very much a real threat."
Of course, no argument there, having nukes is a very real deterrent. Having thousands of nukes so powerful that you could never possibly make use of them without destroying yourself, is a pissing contest.