SC 22.1 introduces the new idea, that it would make sense to be possessive about something that is eternal. This is problematic at least on two levels:
At face value it’s simply not true. Say “the ring to rule them all” in Lord of the Rings would have been imperishable - why would it then make sense to be possessive about it? It would guarantee eternal conflict and catastrophe. Everyone would be ready to kill me for this ‘precious’
Since the argument leads to arguing against atta soon in the sutta: why to sneak in a dubious possessor of atta? If somebody would claim to possess an eternal atta he would have already two eternal entities, namely the possessor and the possessed.
So the sutta here erects a straw-men and is comfortably dis-proving a self-view that nobody claims to have. If the text-book dichotomy of Buddhism vs. Upanisadic Brahmanism is true the sutta should argue against something of the following: “The essence of what I commonly hold as ‘I’ is the same as the essence of the world. By realizing this the ignorance is lifted, and after the death of the body the last veal will be removed and the perfect identity of the two will be established”
This at least is my iteration of Yajnavalkya’s atman-teaching in Brhadaranyaka Upanisad 3.7. Or else, where in the pre-Buddhist texts do we find the particular concept that is argued against? As I have tried to point out already many times, there is no one atman concept in the Samhitas, Brahmanas and Upanishads covering 1500 years (my guess is rather a dozen) and we would need to identify which particular ‘atman’ the suttas are arguing against - or dismiss the Buddhist anatta-doctrine because it’s misleading and tendentious.
See for example the valid question
As SC 23.1 says, it’s arguing against attavādas (atman-doctrines) that don’t give rise to dukkha. But how for example would my attavāda above lead to suffering? Only if I was reborn in a samsaric state - and who could tell if I were? a Buddha/gifted arahant. We arrive at a faith-argument: It’s right because the Buddha said so, not because of a plausible line of arguments.
The fact that the Buddha in SC 23.5 cannot conceive of an attavāda that doesn’t lead to suffering rather speaks for the lack of imagination of the polemic composer than for a truthful argument.
A more sensible (but less detailed) approach towards attavādas can be found in the introduction to MN 8.