The term "good" very much describes something real (and natural), otherwise we wouldn't be able to think of it.

That doesn't seem like a consistently valid rule.

As counter-examples, here are some words that we have thought of, and that we can use consistently and appropriately in context, but that do not describe real or natural things:

• Unicorn
• Witch
• Luminiferous aether
• Bottomless pit
• Immovable object
• Irresistible force
• Philosopher's stone
• Faster-than-light communication
• Ideal gas
• Frictionless surface
• Spherical cow
• Halting oracle
• "Yo mama's so fat she has different area codes for the phones in her left and right pockets"

Perhaps you should read (or re-read more carefully) the A Human's Guide to Words sequence.

The term good, by your description, describes something real and natural. Again by your description, X being "real and natural" is required for being able to think of X.

How does any of this reject the statement that "There is no point in eventspace that has the natural 'Good' property"? (which I infer to be the intended meaning of the statement you can "fundamentally wrong")

That some event, decision, action, thing, X is "good" is a property of the mind, of the map. If there is a Red-Nosed Wiggin in front of you, and knowledge of this fact rates as +2 on your utility function, this is a property of your utility function, not of the Red-Nosed Wiggin or of the spacetime field "in front of you".

With my understanding of proper or common usage of the term "good", there is no case where "good" is an inherent property of the territory that is unbreakable, unviolable, and definitely belongs to the territory itself, such that no map could ever model this as "not good" without being testably and verifiably wrong.

(I don't really expect a response from the author this comment replies to, but would greatly appreciate any help, hints, tips or constructive criticism of some kind on my above reasoning)

Ethics is the problem of actually leading such lives

One of the better definitions, and the one in accord with Aristotle. Though perhaps not the most popular definition.