Vitalik Buterin (38m55s):
"Even if PoS gets 33/51% attacked that's not the end of the world right, the network can fork and continue moving on from there. An attack is going to leave evidence about who participated and anyone who participated in the attack can get slashed after the fact. In the worse case, there could even be a fork that basically does not allow anyone who participated in the attack to participate at all and if that happens then their entire deposit can potentially drain away. So in that sense, there is definitely this kind of nuclear button in the hands of the community if the chain ends up breaking to a 51% attack and I definitely don't expect that the exchanges to want to try to collude to do such a thing."
Dan Larimer (Founder of DPOS):
"I am thrilled to see DPOS proving the concept that the cost of attacking a delegated proof of stake chain is your tokens."
Theft doesn't happen on a decentralized network. In order to get consensus on a decentralized network requires many people working together to agree on one thing. Well, in a theft, the more people involved getting a cut, the less each person makes. Since these blockchains have incentives for doing good, IE getting paid to validate blocks, the theft needs to be worth much more than your normal pay. This is why we have never seen theft by consensus on any decentralized network, even Steem (until ninjamine fund was abused) because theft by consensus just isn't feasible on a decentralized network. You can only steal so many coins before you have so many the market is not liquid enough. Stealing on a mass scale will also scare away any potential buyers.
A 51% attack is not a decentralized consensus. Theft on a centralized network is very easy because the attacker does not need to agree with anyone else about where the funds go, the funds go where the attacker decides. However, as Vitalik points on, attacks on a blockchain leave a trail and the attackers can easily be recognized. The only thing that protects crypto from being illegal securities is the fact that they are decentralized. If they are centralized, they become securities, thus regulated by half the known world. The fact Justin Sun promised to "pump our bags" luring in investors just to steal almost 10% of the Steem supply from the top Steem investors, puts him (Steemit INC) in a very bad spot.
Pretending Sybil or any other type of attack on public blockchains as decentralized consensus is a dangerous precedent to set. If criminals realize they can get away with this, it will happen over & over again destroying our industry. A line needs to be drawn somewhere.
As crypto matures, the more valuable networks will be attacked relentlessly. We will have regulation by fire when it comes to Web 3. A lot will not be able to be regulated, IE a Bitcoin transfer will not need permission, a Hive post will not need permission. However, when it comes to attacks on networks and outright theft, we are still waiting to see how the world will regulate these things. We do know the laws are very murky when it comes to decentralized networks. When it comes to centralized networks however, screaming "YOLO" & slapping the word crypto on the side of your theft won't get you very far.