The problem with FRS/GMRS is that everyone can go to Wally World, get one to use for the same reasons and can listen in to your conversations. Actually, I'm counting on it. I have kept a FRS/GMRS on scan at the house, so that anyone communicating on those frequencies near me will get picked up. And by nature of their range, if I pick them up, they're near me. If someone is coordinating an attack, there's a high likelihood those are the frequencies being used.
Just sayin'
People, especially novices in the field, think that obscurity equates to security. Take for example, the common advice to change the SSH port on a server to something other than port 22, which is frequently targeted by 'script kiddie' hackers. Moving it to a different port may cut down on some of the noise traffic, but a quick scan of the machine will reveal where it is located (assuming one does not employ port knocking).
Radio is the same way. There is a common misconception that if you move off of the ham, CB, or FRS/GMRS bands that your radio traffic will be hidden. The problem is that hardware has gotten to the point where a $20 device like a Raspberry Pi can decode and detect a signal in large swaths of the RF spectrum in real time. A simple FFT repeated will even pull out weak signals, often times including ones that are below the noise threshold. Similarly, there are only a few different ways you can modulate the carrier wave, meaning the number of encoding / decoding methods are finite. If one wants security, you need to encrypt the message somehow, which can even be as simple as a word or phrase in what sounds like a mundane conversation that points to a pre-planned message of meaning. Obviously, one has to be cautious about anything that looks like encryption or encoding in the ham bands, because it's strictly prohibited. That being said, when the balloon goes up, policing the ham bands, or anything that doesn't interfere with an entity that has muscle, is going to be a non-priority.
However, you do raise a good point. There is a high likelihood that any semi coordinated group is likely to be using these off the shelf radios and scanning for traffic, meaning it's fairly close, is a good security move.
