The Securities and Exchange Commission may adopt a disarmingly simple yet effective rule to govern the duties of professionals who make a living recommending investments—requiring them to act in their customers’ best interest.

The SEC, which will formally consider the idea Wednesday, hasn’t articulated such a clear, concise and rigorous standard for investment advice in its 85-year existence. Unfortunately, some consumer activists are advocating that the SEC instead adopt cumbersome and stringent standards. The SEC should stick to its original proposals.

Investors receive recommendations from two types of regulated professionals—registered investment advisers and security brokers. Though both offer investment recommendations, they are compensated by different mechanisms. RIAs usually get their payouts from portfolio-management fees, while brokers are often paid on commission. Neither have received clear regulatory guidance on what their duties to customers entail, and the vague standards that have developed don’t match up.

Securities brokers have always been subject to SEC-mandated customer-fairness-driven duties—they have to sell investments that suit their clients’ economic and investment profiles, but they may recommend those that bring in the highest commission. If those two goals conflict, brokers aren’t expressly required to forgo their self-interest. This can put customers in a vulnerable position, something the SEC’s new proposals would address.