The activation height threshold is what creates the rules, but they're still valid to older nodes. I didn't say that it's a good experience. I said this could be used to destroy Bitcoin and more evidently show that the miners are in control. Invalidating new txns ≠ "Hard fork" hard fork is simply something that is incompatible with older software versions.

Right, so a transaction that doesn't follow this theoretical fork will get mined. Basically everyone can ignore it. The big bitcoin complex would create a disincentive for users to interact with them.

No. I don't know where you got that impression. I said the exact opposite.