[andirk]

> The whole selling point of Bitcoin is that nobody can do that.

It is absolutely possible but not practical. The selling point of bitcoin in this regard is that the work needed to take over the network is relative to the size of the network.

You can 51% a small shitcoin all day. It might cost you $50,000 to do it and now you control a coin that has become worthless because it got hacked by you.

[zirgs]

It's not practical right now, but if block reward and bitcoin price go way down then what are the options? Only the most die hard bitcoin fanatics are going to mine at a loss without getting anything in return. Are there enough of them to prevent 51% attacks?

I would not be surprised if a large crypto exchange takes over bitcoin mining some time in the future. Crypto gamblers don't really care about decentralisation or censorship resistance. They only want the number to go up.