But if there was some brand or some brands of motor oil that are truly bad and could ruin a person's engine, it would be nice to know. For example, maybe there are some people still trying to sell SA or SB oil to people to use in their cars. This was going on, in fact, not so many years ago. SA or SB oil would probably be acceptable only in a Model T, and even then you would probably be better off with a modern oil, assuming the engine was clean.
I do get the impression that some motor oils probably are good for only about 2000 miles, and others that are better in quality will last 4000-5000 miles (talking about conventional oils). Several years ago, I heard of a synthetic oil that allegedly was destroying engines, but I can't remember the name.