Ten years after the collapse of Lehman Brothers, and despite Congress’s efforts to protect Mom and Pop with the 2010 Dodd-Frank Act, the small investor is increasingly vulnerable to shoddy practices on Wall Street.

Dodd-Frank was passed to rein in too-big-to-fail banks and establish new protections for consumers and investors. That included marching orders for the Securities and Exchange Commission to look into reforms meant to level the playing field between everyday investors and the sales agents who try to separate them from their money.

In the years since then, instead of enacting more rigorous requirements for the nation’s 629,032 stockbrokers, the agency has proposed a code that isn’t much stricter than the rules we already have. The S.E.C. has also chosen to do nothing with the authority it received with Dodd-Frank to unshackle investors from contracts that prevent them from taking brokers to court when things go off the rails.

The agency’s official actions and failures to act are not the only problem.

Last month, Hester Peirce, an S.E.C. commissioner appointed by President Trump, threw out a bombshell, signaling that she would support requests from companies looking to block shareholders from bringing class-action lawsuits. Ms. Peirce told Politico that public companies “absolutely” should have the option of demanding arbitration instead of allowing class-wide court actions to proceed.

Today, when shareholders believe they’ve been cheated, they can join together before a court as a class, as investors in Enron and Worldcom did. The strength of such cases is in their numbers — investors can share costs that most solo plaintiffs couldn’t afford — and in the deterrent effect of big judgments.

The commission would have to vote on this issue before a company could institute a rule barring class-action lawsuits for shareholders. Jay Clayton, the chairman and the sole independent on the five-person commission, which includes two Republicans and two Democrats, hasn’t stated a position on barring class-action suits.

Mr. Clayton, however, recently promoted an idea that similarly is favorable to business. He told an audience in Nashville last month that the S.E.C. is studying various issues concerning private securities, including whether they should be made available to a larger universe of investors. The agency now limits private offerings to wealthy investors. Privately held companies provide far less information about their operations than public companies do, making them a risky bet for individuals. Big institutional investors, by comparison, have the tools to evaluate those companies.