Some contracts don't need to be immutable to be useful. A smart contract, even a mutable one, is incredibly useful. It is a state machine that can be programme

Some contracts don't need to be immutable to be useful. A smart contract, even a mutable one, is incredibly useful. It is a state machine that can be programmed arbitrarily to receive funds, distribute funds based on particular rules, etc. Like a DAO, for an example, should be thought of as an LLC-like arrangement. Organizations necessarily evolve and need to be able to change their current framework from time to time, or they're calcified against necessary change. That being said, the rules for conducting an upgrade can still be tightly controlled or placed into a 5 of 8 multisig or a full DAO vote with 10% minimum token supply participating if need be. It's all completely arbitrary and fully programmable. That is, to say, it's incredibly powerful. A mutable contract is clearly not a violation of the contract, as it must be intentionally programmed in that way in the first place, and so it should be clear to any party reading the code of that particular contract that mutability is a feature of the contract and under what conditions mutability is able to be executed. Some contracts you want to be immutable, some contracts you want to be configurable. It's just as simple as that. No need to overthink it, just understand what type of contract you're interacting with and under what terms. That's all.