The Securities and Exchange Commission has been busy this week putting regulations on short sellers, but some officials said that instead of mitigating the crisis, the SEC’s move amounts to little more than shooting the messenger.

The market turmoil over the past year is a result of the housing bubble that burst last year. Short sellers provide a counterweight to the kinds of financial excesses that characterized the bubble, according to a fellow at the American Enterprise Institute, Peter Wallison, a former general counsel at the Treasury Department. “The only real protection against these bubbles is a bunch of people who believe the opposite,” he said.

The SEC will institute new rules to curb short selling in 17 financial institutions, including Fannie Mae and Freddie Mac, and Morgan Stanley, Goldman Sachs, Lehman Brothers, and Merrill Lynch. Yesterday, it also subpoenaed trading records and e-mail messages of hedge funds and investment banks to investigate whether false rumors instigated turmoil on Wall Street.

“I am not sure it will accomplish anything good,” Mr. Wallison said of the SEC’s actions. “What these subpoenas mean is that a lot of people are not going to be sharing information that they have because the SEC might call it spreading false rumors.”

While there may be occasions when short sellers profit from deliberately spreading false rumors, there is no real way to stop that, he said. Besides, he said, “it takes a hell of rumor to take down Fannie Mae.”