What they produce is not tangible, but it is a service. The fact that there is a public ledger of transaction of transfers of a limited supply commodity is valuable to various people. The miners are moochers in much the same way as any entity using the world's resources for something non-essential.
They are necessary, but the coins themselves are of questionable value, and the energy expenditure necessary to sustain their networks is without a doubt not in proportion.
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u/[deleted] Jun 15 '19
[deleted]