> the incentive is hashrate, and each generation of hardware is more efficient in terms of hashrate per joule
That only affects who finds the next block. It will always take about 10 minutes, regardless of hashrate, energy usage, hardware efficiency, number of miners, etc. since the difficulty is adjusted to factor all of those out.
For anyone who isn't a miner (and doesn't care to become one), the only variables which matter are energy-usage and difficulty-of-51%-attack (i.e. double spending).
AFAIK the only reasons to advocate for bitcoin mining are:
- A vested interest. Since bitcoin is a zero/negative-sum game, nobody else should care about someone else's vested interest; if anything they should be opposed (in the negative case; e.g. as a waste of shared resources).
- belief that double-spending is currently unacceptably easy, and would become acceptably difficult given the increased hashrate.
Whilst I don't know of an objective 'acceptable optimum' for the difficulty of double-spending, it would take a lot to convince me that (a) there are credible threats given the current hashrate and (b) those threats would be solved by an increased hashrate. The only threats that even come close would be on the scale of nation-states, or perhaps the largest tech multinationals; yet even if we're paranoid enough to believe they could pull off an attack, I fail to see how burning even 10 times as much energy on hashing would disuade such a level of paranoia.