There is not "one" real anarchist answer. There a so many perspectives in anarchism, that claiming so is really misleading imo.
For many things(meat, PS5, alcohol, medical supplies) its close to impossible or nor feasible to get them via dumpster diving.
And about the "better for the world part" I think you are wrong, but tbh its not like it matters. People should steal stuff because they want it and not because it makes the world better.