Of course people say "but this is silly, obviously we need to condition on health status."

The point is: what if we can't? Or what if we there are other causally relevant factors here? In fact, what is "causally relevant" anyways... We need a system! ML people don't think about these questions very hard, generally, because culturally they are more interested in "algorithmic approaches" to prediction problems.

(This is a clarification of gwern's response to the grandparent, not a reply to gwern.)