Part of the problem is that people use the word immutability when they really mean something else (something less well defined). Check out the post by @phiferd over in here, he does a good job of describing reality and you can see that immutability of the blockchain is well defined, but quite constrained. This definition still holds even if we do a recovery.
So I would say the new information is people gaining a better understanding of what immutability really means, and what Ethereum (or any blockchain) really is in terms of guarantees. Back during TheDAO fork I was one of the people shouting about immutability and slippery slopes, but since then I have spent a lot of time thinking about governance, blockchains, etc. and because of that my stance has changed (though I’m still anti DAO fork to some extent, but for more well defined reasons).
I can’t speak to what the people in the early days meant when they said “immutability”, but as you can see in the link above Ethereum has never been completely immutable (that just doesn’t make sense).
I recommend checking out the writeup I linked above (in this comment), and then restate what you mean by “immutability”. I suspect what you mean is not that you want immutability, but that you want constraints on the ways under which the rules are allowed to change in the future. If you truly want immutability of the rules then I would argue that is against the ethos of Ethereum, since it has long been known that Ethereum will continue to develop as a platform with PoS, Sharding, etc. and that all requires rule changes.
If what you want are constraints on what rule changes can occur, then I recommend dropping the “immutability” argument (it isn’t well defined) and instead argue for how you believe the rules should be constrained. It would also help to argue why you believe that the governance system is incapable of handling this sort of thing in an equitable way.
Never. 
Just because the loudest people believe A, does not mean A is the majority belief. I continue to participate in the discussion because people continue to misunderstand the reality of the situation. If it was just a matter of one group wanting some particular value and another group wanting a different value or the two groups having different predictions on how future humans will behave, then I would have stopped discussing quite a while ago. However, people keep showing up to the discussion with incorrect mental models of reality and that isn’t helping anyone, especially when they propagate that incorrect mental model to others.
Some people have correct mental models of reality and still disagree because goals don’t align or predictions differ. Discussion between these parties has died down a bit because each side has said their piece and there isn’t anything obvious we can do to resolve the differences other than “try one and see what happens” or “accept that we have different goals and fork”.