Sutta is surely not about "self doctrine", but not about "kamma" either, because Buddha did heard nihilistic doctrines before, and here he says "I never heard such a doctrine".
I think the idea is very simple here (and quite stupid): that man thought there is no such thing as "effort". And Buddha was like: "Meh... do you see people putting effort into their actions? Okay then".
I think it might be about absolutes in regards to what we would call free will and hard determinism, but what is framed here as kamma, both in the sense of kamma that is action and kamma that was generated before. From reading some different translators opinions as to what attakáro
might refer to, and by the explanation of a few that seem more informed, the question being posed pertains to whether we truly "act/do" and generate kamma or if we are eternally pulled along by kammic causalities like puppets with no volition at all, for in such an instance all conditions and causes are determined by an "other-doer" solely, no kamma is believed to be generated in the last case.
The "certain Brahmin" proposes two sort-of extreme idiosyncratic positions in this regard, both of which the Buddha labels as such ("I have not, brahman, seen or heard such a doctrine, such a view."
That is just what I gleaned from some of the translators I read though.
But that interpretation also agrees with what you say. If the certain Brahmin thought that there was absolute kammic determinism from kamma originating from anything "other", and that there was no kamma generated at all by anything presently or dynamically acting/doing, then it would follow that liberation through own-effort would be futile and one should just lie down and whatever happens was fated to be from the beginning. That's just one take though.
That interpretation is based on the belief of some translators who say that the verb káro
doesn't just mean the exact same thing as the English verb "to do" or its noun-form "doer". It is also said to mean "maker (of action)" as in "maker (of kamma)" or "generator (of kamma)". So "self-doer" and "other-doer" could also be equally correctly rendered as "self/other-actioner" or "self/other-maker (of kamma/causes)".
To the user "theY", is the above explanation what you were trying to communicate by saying:
theY wrote:In Attakārī Sutta:
Brahman concept is "Cause does not has any effect".
But buddha concept is "every cause have many effects".