Having just been through the SMS rollout in New Zealand as a part 135 operator, 90% of the benefits come from 10% of the program. The cost of the program meant that we postponed avionics upgrades and had reduced staff levels, so we traded some clear and obvious safety benefits for some cargo-cult safety theatre. In the real world there are no free lunches, and extra costs have to be absorbed somewhere.
And aside from just the extra costs being a drag: there are many examples of regulation forcing us into the less safe options because the safer options are either legally unavailable or totally cost prohibitive.