Eventually, the blockchain will be hacked.
I know it is decentralized and the hacker needed to have control over 51% of the network to 'hack' it! BUT, like any other hack, maybe there is a way we don't know about YET! Everything is 'hackable' from the moment it is online!
What do you think about this?
AFAIK having 51% of the network hashrate does not guarantee control of the network.
It simply implies that one has greater chance of solving a block instead of the rest 49%.
The other 49% though still has great chances of solving the blocks themselves.
As you can
see here 21 Inc. has only 4% of the network hashrate yet they solve blocks too

Now, if an entity or group was to accumulate more than 51% of the network hashrate it would be in their best interest to actually use that power to solve most blocks and get the reward.
Remember, that they cannot control Bitcoins they don't own already, so, think about it, what would you do?