Have you ever considered in forming an alliance like OPEC to limit the hash rate race?

I just saw Bitfury said that their cloud service would only add hardware based on demand, is this a trend towards more cloud based service?
It's funny to read it from mega self miner.
No, it's illegal.
How is that illegal?

It is just a consensus (if it ever can be reached). Even pools can be allied together to protect against a faulty fork in 2013, and against potential 51% attack if it ever happens
Imagine a vendor that have leading semi-conductor process 10nm, he can limit his production scale at a certain level so that the network hash rate increase slowly. He then could start a cloud mining service and sell the hash power at market rate, which leaves him large margin to deal with market volatility. I think that is what Bitfury means
In the USA there is an antitrust law preventing companies from joining together to set / fix prices and supply. Its to promote fair competition for the consumers.
Except that in practice monopolies and cartels are the rule rather than the exception. Many are protected territorial monopolies,such as power companies, others just invested in America by buying senators and (potential) Presidents, such as the very obvious Health insurance cartels.
Frankly, the "antitrust" laws are only ever invoked against companies that THREATEN protected monopolies. It's a really poor argument.