The MEK was an opposition group during the time of the last Shah. In the 1978-9 revolution, they enjoyed a lot of support. They eventually diverged from the new, clerical rulers, becoming hated by the latter. But, since they sided with Saddam Hussein's Iraq, invading Iran alongside his forces, they have lost all support within Iran. Now, they seem to have significant, foreign funding and support, frequently featuring established American and European politicians in their glitzy events. They frequent Twitter with many accounts which seem to work in concert--and, reputedly, from a base in Albania! Historically, their ideology comprised a blend of Islam and Socialism, but they have long been described to be more a cult (in terms of their disturbing effects on their followers) than a movement.
When, inevitably, the theocracy falls in Iran, will MEK candidates get to run in elections? So long as they accept the secular, democratic constitution, they must.
Likely, they won't get any votes--being as despised as they are. But they must be allowed to run. To decree otherwise is to defeat democracy.
If an argument of _principles_ fails to convince you, a look back at 1978 _ought_ to! By not allowing different voices to speak, to run, and to vie for people's votes, the Shah created a vacuum which only the hoi polloi's magical superstitions (aka faith/religion) could fill, in lieu of an ideology. The Left, too, would have had to compromise on their theories--had they been allowed, electorally, to come to terms with the pragmatics of popular support.
Similarly, will a Hezbollah party get to run?
I've heard that, by the regime's own account, about 7% of the populace support it. Other figures I've heard go as high as 10% to 20%. After the overthrow, these people will vote. For at least the short term, they will vote for Islamist candidates/parties. It is very likely that a Hezbollah ("Party of God") will be formed--but one which will have to accept the secular constitution in order to run for office.
This, too, must be allowed to run. These people are citizens; they will have the right to representation. And, like any other's, their candidates will have to negotiate and compromise--to legislate, to get media coverage, to get things done. The inevitable convergence towards a mainstream, or mainstreams (depending on the electoral system), is frequently a corollary of democracy.
The late, great Dr Homa Nategh, said it best: You're not freedom-seeking, if you're not seeking freedom for the other.
Everyone thinks of him/herself as freedom-seeking, but you're not freedom-seeking if you're not seeking freedom for your [ideological] opponent.