I'm always of the belief that if someone wants to kill themselves (cigs, sugar, etc) or gamble their money away, or anything similar, let them do it, it's not the gov't job to keep them from that, it's the gov't's job to make laws to punish people who do things that affect other people. Gamble all your money away till you're living in a cardboard box on the street? Fine. Steal money from someone cause you need to gamble? That's where the laws are.
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Yes, they cover the cost of PRODUCING the game, but not maintaining it. Loot boxes is a small price to pay for new maps, heroes, updates, etc all being released.