There's quite a difference between radicalism as defined by the Inquisition, and willingly serving the forces of Chaos, which is what the OP was talking about. So my point still stands.
Perhaps you're familiar with the saying: "The road to hell is paved with good intentions?"
Also, willingly serve the forces of Chaos doesn't necessarily mean that your character has an innate evil wish to drink the blood of young puppies or murder thousands of innocent people only to please Khorne. In fact, I'd say it's quite rare for people to willingly serve the Chaos gods from the very beginning. It just starts with something, and then a Dark Pact is struck somewhere down the line, and the more and more you will owe the forces of Chaos something, and they'll get you to commit worse and worse atrocities that finally your sanity gives out and you'll become the puppet of the warp.
But it all just started with a normal person that wanted something out of his or her reach. Perhaps it was eternal youth? Perhaps it was extreme wealth? Perhaps it was trying to save a dying loved one from certain death due to disease?
These "ambitions" if you will, have a way of shining brightly in the warp, and sometimes a daemon might heed the call and put into motion it's machinations in trying to strike a Dark Pact. Perhaps through using his other corrupt puppets in making sure that this person who has a wish get a hold of the means of contacting the daemon. Perhaps by "accidentally" dropping an old book describing daemonic rituals outside the door of the person with a wish's home or some other insidious plan?
It's a matter of desperation really. Make sure a person is desparate enough and that person will do whatever you ask of them, as long as you start out small in your requests (like perhaps steal a trinket or fool someone into giving his money away), then you can move on to worse things like sacrificing virgins in the name of a Chaos god or commit all sorts of terrorism. The victim's sanity and purity will slowly wither away, and the more insane an corrupt that person get's the more willing he or she will be to serve their dark masters.