What happened? Did the "dumb stat for dumb people" comment get removed by the mods?
Like most stats, they are better understood when given context. You'll have games where a player plays extremely well, and still ends up on the minus side of the ledger. and games where a players is dogshit and ends up a plus. But when those numbers are smoothed out as the sample size gets larger, if a player is a minus player over a sizable sample when compared to other players on his team, you can be darn sure it means something.
How long has plus/minus been tracked now? 40 years? 50? Used by many a former player now a coach or manager. Former players who know exactly how it feels when they come out of a game on the minus side of the ledger if they take any pride in being well-rounded players who contribute in all facets of the game. To them, you can be darn sure it matters.