I think the horrible PMs are one of the funniest aspects of the game.
Once you are comfortable with the game, and aware of the tools for dealing with anything really abusive, then there's probably less reason for wanting this to be available, although I suspect that some would leave it off, especially if squad members were exempt.
But when you are just starting out in the sim and not sure if you fit in, getting a rant and rave PM can be very unnerving - and after a couple of them, I know I seriously considered dropping AH and going back to WWIIOL, despite dissatisfaction with the air to air portion of that sim. I honestly think that it's in HTC's better interest to ensure that there is a delay before new players are exposed to them - but that's just one man's opinion.
Ideally, I think that some arena's (training, DA) as well some players (trainers, squadmates) should be able to PM and VOX cross country regardless of the checkbox, however.
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