^H^H^H^H^H^Hcosts -- FTFY. It's not a waste if you actually got something for it. e.g. your chemical ICE in your car produces heat that is useful in cold weather. Not waste heat if it has utility. Electric cars have to spend electrical energy to generate the same heat.
That said, the fact that this keeps coming up would indicate that there's definitely a marketplace for a coin that costs less energy/emissions for the same features.
Other coins have been proposed that either reduce the amount of computation (PPC) or increase the utility of the calculations (XPM). Note that those have existed for a long time and don't require an ICO. Using storage space as a (hopefully?) less energy-intensive contest to replace PoW is interesting although I suspect that Chia isn't truly novel here either.
We're just in the process of coming up with alternative ways of doing what Bitcoin does in a more efficient manner, much like what ICE innovation has done and continues to do.
What's the baseline for a corresponding transaction? Maybe that's a credit card which will cost (not waste here either) 1-2% of the purchase price. But even that's not quite fair because the merchant is taking some risk on this purchase that usually amounts to some additional cost. Also credit cards can't be used to secure transactions of >= millions of USD (and if they did it would be at a significantly higher cost). Bitcoin transactions at the low end of that spectrum are prohibitively expensive, though.
It doesn't matter if bitcoin is still the best way to spend money ever. The mining is a waste, a tragedy of the commons.
A proof of stake system that consumes virtually no energy and charges negligible fees (if it works)?
But to further the debate, how would you evaluate it in these terms ("waste"/"extravagance")? Would you stipulate that it has value or that it at least has utility? What sort of analogy or baseline would you compare it to, so that we could evaluate how efficient or wasteful it is?
Also bitcoin has heavily failed in its "decentralized" dream, as most of the hashing power is under the control of very few individuals.
This seems to leave its only purpose as some sort of strange "HODL" and speculation machine, and I don't believe that is worth burning an entire small nation's worth of power to promote. In fact, my opinion is that such a system is actively harmful.
Even if you believe that bitcoin is not some eternal pump and dump, that just leaves it as a valid investment vehicle. I don't consider a single investment vehicle to be worth the energy spent to maintain "trust" in the chain