If you hear the apparent voice in your head and if you believe it is sent from the supernatural existence, it is quite dangerous as you are likely to follow the order, especially when it is actually the voice sent by the spies through the electromagnetic wave.
The brainwash can also be conducted by the one similar to the inner voice, though it is less effective as you are not subject to follow the orders. For example, your friend in front asks you to kill someone, do you follow? There might be a special circumstance to do so, though the majority of us just ignore or contradict the idea. That is basically the same for the inner voice, that you can dismiss it as a crap.
However, you might believe it is the right thing to kill the targets when you are manipulated to suffer from paranoia. Your emotion can be exaggerated to the bad direction when confronting some issues.
For example, your anger can be manipulated when you watch the news about the religious issue. The spies keep this manipulation every day for some months, you might believe you should do something for that matter. Your thoughts and emotions are totally manipulated through the electromagnetic wave, though the manipulation is so covert for you not to realize.
It is just an emotional control to become angry with the specific issue and you consider it quite injustice which your inner voice talks at the same time. Those two combinations are easily manipulated by the electromagnetic wave capability, though we still do not realize its capacity.
Or, the spies can create the special targets in your mind, and eventually, you believe you should attack them after several months of brainwash through the electromagnetic wave. All they should do is to cause paranoia and hatred, which should take more time than to brainwash the subjects through the apparent voices, though it definitely works with a lapse of time.
This operation is a time consuming, while it can be more covertly conducted than the apparent voice. At the same time, some of us do not believe the apparent one in any way, as it is apparently external. The other one is quite similar to the inner voice and hard to tell it is sent from the outside, which means this capacity works more generally to the people.