How can we overcome this monopoly? How does this effect the whole concept of "decentralization"?
It's because humans are idiots and think that the new boss will be different than the old boss.
Bitcoin doesnt change anything fundamental about humans, it's just an instrument that can be used for good or bad.
Just like a nuke, it can be used to stop asteroids from hitting earth, or it can be used to destroy Hiroshima. It's humans choice.
So Bitcoin will probably be used for evil too, it is already being used by scammers, and who knows who. So people who think that BTC will solve everything are stupid.
It's humans that are the problem not Bitcoin.
"If the wrong man uses the right means, the right means work in the wrong way." This Chinese saying stands in sharp contrast to our belief in the "right" method irrespective of the one who applies it. In reality, everything depends on the person & little or nothing on method. The method is merely the path, the direction taken by a man; the way he acts is the true expression of his nature ~CG Jung Alchemical Studies