Getting PTSD from a video game is as likely as getting a whiplash after crashing in a racing simulator.
Somewhere along the way your brain should be aware that what you doing is not real, unless you have some sort of psychological disorder. So no, I don't think the average adult brain will have problems separating reality from video games.
However, kids appear to be highly oversensitive to video games
even without VR, so selling VR sets to kids is probably a bad idea. For one thing the brain is not fully developed until you are at least
25, which supports this argument.
As already pointed out, VR has most of its value in applications outside of the world of gaming, for example it might be very useful in physiotherapy for kids and adults alike. It can also be very useful in education and in professional work, from architecture and medicine to astronomy and archaeology.
I think video gaming is just a small and limiting part of VR's potential.
Edit:
As far as video games go VR will be focused on first-person games; mainly FPS, horror, Minecraft and simulators.
In other words it mainly affects a few gaming genres and franchises.
So we will still have our strategy games, third-person games, rpgs, platformers, sports games and so on.
And even
with VR developers can't afford to make VR-only games, they still need to offer regular gaming options if they want to reach decent sales figures. Most gamers cannot afford a VR set, let alone
be willing to buy one.