The Basij are clearly not a renegade force. I would compare them to the Nazi brownshirts. They are a security force composed of plainclothes thugs. The regime is very smart. They know that if you send in the army to shoot into crowds of peaceful demonstrators, you have a massacre, and the regime will collapse with that kind of open confrontation.
So their strategy is to infiltrate these crowds with plainclothes individuals who then, at the appropriate moment, begin to stab or club various individuals. You have savage beatings and savage stabbings. The message is very clear: it's terrorization. They want to send a message that protesting in the streets will be dealt with so harshly that it's not worth it for you to come out of your home and participate.
The Basij are a paramilitary unit under the Revolutionary Guards. The Revolutionary Guards are directly subordinate to the supreme leader. Just after the recent events, the Revolutionary Guards acquired the telecommunications company in Iran and they acquired one of the largest iron ore mines in the Middle East. So we're moving towards a military state that is dominating all the resources of the country for its own benefit. They have a network of patronage, which keeps people happy.
The Basij are not just volunteering to come and beat people; they're paid money. By some accounts, they're paid about $200 a day for beating and stabbing people. When you have unemployed youths who are given $200 a day, which is a lot of money, to come and beat people at will and who on occasion are allowed to rape people as a bonus, then you can see the way in which that regime of terror is being sustained and how the structure of the economy is used to sustain this kind of authoritarian rule through terror.