I would highly doubt that it is impossible for them to access your PM's if they feel the need to do so. They have a need to moderate. Just imagine all the things people with no interest in BeamNG could send via PM if there was no way to access or moderate it.
You are quite clearly very very naive if you think any company that doesn't specialise in private communication is going to allow people to communicate in total privacy. Since it isn't in the interests of the company to deliver that service and they would rather not get shut down because of people sharing illegal content via their PM system. And before you start to ask, no, your private messages through Facebook, Twitter or any other social network are not private from the companies that run them. Including email. If you live in the US I believe that your ISP is allowed to watch everything that you do anyway and even use techniques such as deep packet inspection to inject content onto the web pages you visit. So unless you are using something very specialised such as Signal by Open Whisper Systems none of your private messaging is private. And after all of that providing someone is willing to put in the effort any communication system can be compromised.
Well I should re-word that to punishing you because of PMs unless it's like death threats. Total privacy doesn't exist. Yes, I know.
Reading the last couple of pages in this thread has made me lose even more brain cells. This fucking forum, man...
They can, but as @WalrusVersionofCRAZYRACER said they only do it when they get reports. I believe Dunkleosteous got reported and the mods went into the conversation and found 39 pages of pr0n. Moral of the story is, don't be an idiot.
So that's who that guy was? Seriously Dunkleosteus? And I only have one expired warning point. That looks delicious. They have to be able to see PMs for security reasons. You never know, if they didn't, somebody could take advantage of it for very nefarious reasons. Like others have said, as long as there aren't any red flags raised, it will be fine.