... because it breaks the basic fundamentals of a block chain. A block chain is supposed to fight against roll backs not support them.
Sure, the core team / devs are using the rollback for good. But will that always be the same in the future? It's an avenue for abuse and one of the primary reasons ether isn't going to take off.
The point is, if the core team made a change that's widely unpopular, clients would just refuse to upgrade to that version.
Discontent users simply switch to a different branch maintained by different developers. If there's enough consensus, people will call it "real" blockchain and the other one will be left behind with few users and hence no meaningful way to spend the balances.
Exactly. You need overwhelming consensus to change the rules safely.
Bitcoin is currently in a state of disarray because groups of developers, miners, industry and users disagree on fundamental aspects of the scaling debate.
There are no fewer than 4 competing Bitcoin fork proposals on the horizon, each one with an unknown number of supporters. The only thing we can measure accurately is "signaling" in blocks, where miners declare their intention to follow one fork when the designated time comes: https://coin.dance/blocks
However, there is such a thing as "false signaling" for strategic reasons, and hashing power can rapidly shift (or just appear, if new mining rigs come online) in favor of a different proposal at any time.
This is indeed a deeply flawed voting system. In contrast, Ethereum still has a capable leadership with sufficient consensus that they can propose and execute hard-forks whenever they feel it's needed, without this level of uncertainty and drama.
Sure, the core team / devs are using the rollback for good. But will that always be the same in the future? It's an avenue for abuse and one of the primary reasons ether isn't going to take off.