The MEK does not have the capabilities to support a large-scale revolution. The MEK's activities have been reduced in recent years and it faces a growing problem with recruiting younger generations.
From: International Affairs Review
A many prominent politicians within the United States from both sides of the aisle support removing MEK from the State Department's list of Foreign Terrorist Organizations (FTOs). (...However), the complete lack of support for the group in Iran, growing logistical issues, and the terrorist tendencies of the group all accentuate the unnecessary risks of overtly supporting this organization.
First, the group lacks any significant support from the Iranian public and is despised by most. This reality stems from the Iran-Iraq War that lasted from 1980 to 1988. During this conflict the MEK sided with Saddam Hussein and openly waged war against the Iranian people, a betrayal that was never forgotten. If the U.S. aligns itself with such an internally despised organization, it will significantly undermine democratic efforts and stability in the country.
Secondly, the MEK does not have the capabilities to support a large-scale revolution. The MEK's activities have been reduced in recent years and it faces a growing problem with recruiting younger generations.
Coupled with this, the U.S. military has weakened the MEK's militia and limited its operation to Camp Ashraf in eastern Iraq. However the Iraqi government's decision to shut down the camp by the end of the year uproots the MEK from its only position near the Iranian border. These are but a few of the logistical issues that restrict the MEK's involvement in Iran.
Lastly, the MEK is a terrorist organization that has knowingly killed Americans. This organization actively promoted and supported the U.S. embassy takeover in 1979 and opposed releasing the hostages.
If the MEK decides to engage in terrorist activities in the future, the aftermath would be detrimental to the United States. The high risk of such an event makes legitimizing the MEK illogical.