In the case of flare gas, it is a byproduct of gathering oil that is unavoidable. The oil is economically worth collecting, but the extra gas is not. I think this can be more finely split into natural gas vs methane-- sometimes the natural gas is worth collecting, but the methane never is.

You could argue that there should be laws to force the methane to be collected and used elsewhere as a condition of accessing the oil. That might be overall better. But prior to bitcoin, that perfect solution was not really implemented. In this sense, bitcoin mining of flare gas is a step forward.

Note that the argument is not just that economic value is created by mining bitcoin, but that running the gas through a generator leads to cleaner combustion and thus less greenhouse gas emission than simply lighting the gas on fire. In this sense, the bitcoin flare gas mining operation by itself could be considered carbon negative (again, surely all bitcoin mining is not). The bitcoin mining pays for the generator. So bitcoin mining is giving the industry a subsidy that enables reduction of environmental harm. It is not perfect, but it is an improvement.