Believing that it works means simply accepting the average return of the market through index funds as you said, which sounds reasonable to me, but it is admitting defeat that you can't beat the market in the long run.

Seems to me everyone would agree it works in general and the trouble starts when you try and do better than it.

Is your reason for not looking for inefficiencies to exploit and do better the fact that it takes more time than you have to devote to it, don't believe its possible in the long run (i.e. largely luck), you require some special insight other people don't have, other?