I appreciate the title is wrong, but no reason not to add the correct context.
Yes and? That they did it for free instead of for pay is supposed to make it better?
The difference is not really clear in reality and can get blurry quickly. Informants can also be ordered to do more active things to get information - or spread missinformation, or be ordered to do other active things. Simple things like luring a person to a party, or using their influence of position to prevent or make something happen (punish/promote a student/worker, make a certain result go away, ..).
So the majority were likely passive informants with the job of writing reports, but not all of them. And to me it rather would matter if they took the job voluntarily or were forced to do it.
(the main intelligence agency work),
like luring a person to a certain party, spread (wrong)information, steal certain things,
Best that can happen. People will be disappointed but that's it. If the IMs are still alive it can get really ugly really quick.
I decide to believe that communism doesn't look like a nice system and I decide to believe that I really don't believe those saying: "this time we'll make communism work".