With the Jan 6th prosecutions, the DOJ put the Fear of Prison into the militant movements and made it clear that there is no such thing as safety in numbers: you will be caught on camera, and you will go to prison.
Perhaps some may be deterred by "fear of prison". But then you sill have to deal with:
- People who still think "they won't be caught", and perhaps use the Jan 6 prosecutions as guidelines of what not to do, such as "maybe I should do better to hide my identity". (Remember, the Jan6 terrorist attacks was probably unique in the amount of coverage that was given to the situation. I suspect most terror attacks in the future will be against "softer" targets.)
- People who think "even if I get caught, once my side is in power I'll be released and treated like a hero".
- People who look at the relatively light sentences given to some of the terrorists and think "its no big deal if I get caught"
- People who are willing to martyr themselves for the cause
Most militia type groups assume they have informants in their midst, and they are probably right.
I am sure they do have informants involved in many of the right-wing terror groups. But that may not matter in the case of:
- Lone wolf attacks (or people working independently or in small isolated groups). Example: See McVey, Timothy
- If the federal government is under the control of someone who works to minimize the problem. (Remember, when Stubby McBonespurs became president, he ended some of the programs that were meant to deal with right-wing extremist violence.)
- If the level of violence rises to the point that even with informants, law enforcement cannot deal with all the cases
Informants are not perfect. A terrorist group that has sought to operate as small 'cells' may at least be partly immune. And those dealing with potential acts of terrorism have to act appropriately when they do get information. (There was plenty of warning that SOMETHING would happen on January 6, but the government did not plan for it very well.)