Assuming HFT/coin mining do indeed contribute in these ways, are there less energy-intensive solutions that could produce the same or a similar effect?
I think it's completely reasonable for there to be regulations that limit the global impact of activities (e.g. emissions, global warming, chip shortage) for the good of the general population, especially in relation to how much tangible good they produce. That's the whole point of governments and regulations to begin with; see also, things like leaded fuels, or asbestos, or trust-busting.
