[spuz]

Profit from mining (for example Bitcoin) does not scale linearly with the amount of money you put in. If only a few miners control the hash power of the network, that will discourage use of the currency and drive the price of it down. It's not in the interest of miners to control > 50%.

[RodgerTheGreat]

It's not in the interest of miners to admit to controlling > 50%. If you can do so in secrecy, it's a pretty fantastic racket.