The current regime in Iran is one of the three nations designated as the greatest threats to the United States the the rest of the world. It is one of the most unstable regimes not just for the world, but by suppressing it's own people. Not only that, it is a nation that is seeking nuclear weapons.
Thus, to think that by supporting the opposition we will diminishing our ability to negotiate with the current regime in Iran about getting rid of nuclear weapons is absolutely hogwash. You can think you can negotiate all you want with this thug regime, it will never stop seeking nuclear weapons.
The only hope of the U.S. or anyone else ever being able to negotiate regarding nuclear weapons is with a new regime.
Ronald Reagan learned that by supporting the people of Russia he strengthened the opposition and actually increased his negotiating power with the regime in power in Russia at that time. That, in itself, is the same kind of strategy the U.S. should take today in Iran.
The U.S. should support the people of Iran, the only hope for democracy in Iran and stability in the Middle East.