Exactly, going back in blockchain is an unwritten rule. It shouldn't happen. If this happens it clearly means that the miners which chose to do so act in a centralized way for their own private benefit(a real life revolution always has couple of central leaders without which the revolution would fail). The small miners will not have a choice. It will be mostly decided the by pools owners.
Going back into the blockchain is a centralized decision no matter how you look at it and who takes part in it. Unless there is a major bug affecting all users, the rolling back shouldn't be an option.
It's an unwritten rule because it's not even a rule. Plenty of cryptos, including Bitcoin, have rolled back before. You are the fundamentalist taliban of anarchism, you are idolising the ideology of the so-called "free market" in the face of overwhelming practical and ethical reasons to take a constructive decision to freeze a single transaction on the blockchain. The solution the NXT dev posted does not even roll back anything else than that single transaction. No, this will not erode trust in NXT. If anything, it will protect trust in NXT as the NXT dev is taking action to protect his own creation with literally no ill consequences (except if you're the hacker), and you are standing on the side of the road yelling at a cloud.
Besides, this is the free market in action. It's up to users to start using the new wallet, and we can collectively choose to ignore that transaction. There is nothing more democratic and decentralised than this. What in the hell are you complaining about?
That, or you were planning on stealing some crypto yourself and are hoping to establish a cultural precedent for you to get away with it.
you are creating a precedent here. It is totally a centralized decision which will set a precedent in the future when and if crypto will be accepted as global currency. It will create the option for big entity to bring his mining power in action whenever a rolling back will be in his favour. This is an unwritten rule. Crypto stands for irreversibility not for lets take another look and if it doesn't suits us lets rewrite history by using latent forces of mining whenever a rolling back suits us.