Softforks cannot add more coins into the network, they can, at most, restrict earlier valid transactions.

It's always been known that someone with over 51% of the power can rewrite the blockchain, but only within the rules of the Bitcoin nodes.

For example, a softfork could never spend coins from your wallet without your key, it could never make more coins or delete a users balance.

This is a good post on the difference: http://bitcoin.stackexchange.com/questions/30817/what-is-a-s...

51% certainly gives someone a lot of power, but it's power with limits, and the limits are the rules coded into every Bitcoin node.