Even with locations, if you tell your location in IC means ie. through a radio and someone is listening in, it can create more RP because that person might come over to where you are whether they are another rebel, CP or whatever. With the OOC pm, no one knows except you and the other person that you are going to meet up, which can be argued that you are getting an advantage because you have that knowledge that "oh, no one is going to intercept me or do something at this location that is not to my benefit" and it may not bring around more RP.
I'm sorry, but offering the radio as an alternative is a really disingenuous way of trying to invalidate my argument. The radio requires you to grind resources and level your crafting skill, neither of which are roleplay-based whatsoever. There is no way to acquire a radio purely through roleplay: At some point in time, it had to have either been grinded out by a player or purchased by someone who grinded it out for you (and you also still have to grind to get the money to buy it, btw!)
Secondly, radios are, ICly, highly illegal items. This means that you essentially create a scenario in which certain groups and factions are able to use this "IC pm system" as you're trying to make it out to be, while at the same time other groups and players have to risk their items and in some instances
their entire character just to use the system you provided due to the in-character considerations. The phone systems put in place by Willard are no better, and in many instances even worse: There are only a few select areas in which players may use them, and they aren't equitably spread across the map, allowing for easy access amongst all parties equally. They are only in areas that are generally off-limits to rebellious players.
I think this scenario would hold a lot more weight if radios were not restricted to those who strictly wanted to go down an illegal or rebellious path, or if mobile phones existed which allowed players to "ICly dm" one another via such a device.
Thirdly, do you have any examples of the current radio system being used to intercept transmissions, and then having those transmissions be utilized to further RP in any way?
Fourthly, this statement: "oh, no one is going to intercept me or do something at this location that is not to my benefit" is assuming the worst from people for no reason. If these sorts of individuals exist, and are using systems in a way to avoid RP, you can simply investigate to see if it's rule, and if so, warn or ban them from the server like you did me. People who do this on the servers I originally took this idea from are caught very easily.
EDIT: Forgot to mention radios make a loud-ass noise whenever a message is sent, making it nigh impossible to use one in any area that has even a miniscule police presence.
You are unable to use one discreetly. Trying to make a highly illegal, obnoxiously loud, and hard to get item as a reliable and effecient alternative to doing basic coordination like saying: "Hey man I'm around, wanna RP?" is super disingenuous to my argument.