The second you say “I ought to…” or “I ought not to…” you rise up out of the world of mere materialism and step into a world of morals and ethics.
Sure, you can get “morals” and maybe practical action from the natural world.
This is not an easy issue to brush aside.
All the human beings that history has heard of acknowledge some kind of morality; that is, they feel towards certain proposed actions the experiences expressed by the words ‘I ought’ or ‘I ought not’. These experiences resemble awe in one respect, namely that they cannot be logically deduced from the environment and physical experiences of the man who undergoes them.