Aside from the electricity usage concerns, this presents a big risk for bitcoin. Centralization of mining power was one of the biggest issues of the BTC vs BCH

Aside from the electricity usage concerns, this presents a big risk for bitcoin. Centralization of mining power was one of the biggest issues of the BTC vs BCH debate. BCH proponents wanted bigger block size. While BTC proponents argued that bigger block size will lead to centralization, as not everyone will be able to propagate bigger blocks. So, if Bitmain et al. do end up controlling 90% of the hashing power, they might be able to control voting and other aspects of the network. They could prioritize their own transaction, pay lower fees etc. Now this will lead to two things. First, cryptocurrency circles love perfect game theory. The argument is always going to be - Bitman etc are not going to harm the network even if they take over. The reason being it will always be in Bitmain's favor to ensure bitcoin's sanctity. If things go downhill they will lose tons of money and mining worthless coins. So, people should not turn away from bitcoin. Second, we are talking about human nature and not a perfect prisoner's dilemma. So, Bitmain etc will be sneaky and maybe even vote against some BIPs they don't like. Some of their behavior will warrant people to leave bitcoin. But, then bitcoin supporters will bring up the first point again. Game theory, hence HODL. This will at the end become a roundabout discussion: Step 1 - News - Bitmain etc does X which is very bad. People should leave a centrally mined coin. Step 2 - Bitcoin supporters - Game theory says Bitmain etc wont harm the network as their coins will worthless too. HODL. Rinse and repeat. The irrational belief in perfect math and game theory will give lot of leeway to anyone who captures Bitcoin's mining power.