It is against stakeholders best interest to roll back the chain on people who are unpopular or doing unpopular things.
Delegates can have all sorts of motivations or be coerced into having all sorts of motivations. I could easily imagine a scenario where 60% of stakeholders and over 80% of delegates preferred to implent changes that incorporated blacklisting to go mainstream , and you know for things like "think of the children!"
If 80% of delegates act differently from the wishes of stake holders, they can be voted out. So, I think the only major worry would be someone gaining 51% of the money supply and attacking. Even then, it would be a stupid waste of money, as you are killing something you own a majority in and spent a lot on to gain that stake.
If 60% of stakeholders decide something should be done differently.. Then that is there choice, no? The ones that don't agree can sell their stake and start a new chain on their own. That makes sense to me because Bitshares looks at cryptocurrencies as a business. If you own 51% of a business, you should be able to do as you please. It is like how a democracy would work or business would work in the real world.
On the other hand, if someone gained 51% simply to attack the coin the non attackers could just move to a new coin and start over. I don't see how that is a bad thing. Furthermore, it is highly unlikely. For one there is almost a certain likelihood that there will not be 51% of the coins on the market to be sold at any point in time. If there is not, then multiple users need to be hacked to gain 51% of the stake.
I just don't see how it makes any sense whatsoever for someone to attack th e chain after gaining a 51% majority, as they would need to spend a fortune to do so, or hack multiple people. There are also cold wallets, which is one thing DPOS allows users to do that other PoS implementations don't and remain just as secure as if the funds were in hot wallets.