No, you don't have to. You don't need any kind of fancy utilitarian approach if you're willing to have principles and actually stand by them.
Murder is wrong because it deprives another person of their life for no just cause. Miners buying up GPUs only means that someone else has to pay more for them instead if they want one. It's no more immoral than people paying more for beach front property and driving up property values. What someone else does with their money isn't any of my concern and neither is any personal behavior of their that doesn't damage me or cause me harm. No utilitarianism required.
I'm not even going to try to whine about things like environmental damage somehow causing me personal harm. I'm sure that my own air travel puts out more CO2 than some people with light mining setups. No one here is going to claim that air travel should be banned and I'm quite sure that anyone who did would get funny looks. People like to make these sort of arguments, but rarely apply those same arguments to themselves or their own life. If they actually do, there's usually some form of mental gymnastics to justify it.
Frankly gaming is every bit as much of a waste as mining. A GPU rendering pixels to amuse you isn't fundamentally any different from that GPU calculating hashes to solve math problems if that brings you satisfaction in the form of some digital token. The only difference is that the mining can be done without your direct attention. Of course we could draw parallels of running bots in games to attain some reward. Of course the very same gamers that want to ban mining would have a conniption if someone proposed banning computer gaming so that GPUs could instead be used to fold proteins in order to find better medical treatments.
That's why the argument against cryptocurrency often falls flat for me. It's typically loaded emotional appeals, terribly flawed reasoning, or any number of other poor arguments that crumble under casual examination. Even the countries that have been banning currencies like Bitcoin or Ethereum have no problem creating their own, fully government controlled currencies. The genie is out of the bottle and it doesn't look as though it will ever go back. I certainly wouldn't complain if cryptocurrencies went away and I could get a cheaper GPU, but I'm not going to call for them to be made illegal, because what argument would I have when someone wants to make something that I enjoy illegal?
