They don't own the computer power. It comes from the miners who join the pool.
The 51% attack problem is something that needs to be solved for bitcoin. But it isn't as bad as you think it is.
I used to think that someone who took over the network could spend my bitcoins even without my private keys. But that is not true. The actual attacks possible with 51% are significantly more minor than stealing bitcoins.
Really? If the pool only has 51% of the mining power but gets 100% of the block rewards, pool members would get coins at double the normal rate. I don't see a lot of people leaving in that event.
The 51% attack problem is something that needs to be solved for bitcoin. But it isn't as bad as you think it is.
I used to think that someone who took over the network could spend my bitcoins even without my private keys. But that is not true. The actual attacks possible with 51% are significantly more minor than stealing bitcoins.