That's the wrong question to ask.

The right question is whether I have made any important files world-writable.

And the answer is “I don't know.”

So, containers.

And I run it with a special user id.

Well, let's say you weren't on a machine with hundreds of users. Let's say you were on your own machine (either as a solo dev, or on a personal - that is, non server - machine at work).

Now, does that machine have any important files that are world-writable? How sure are you? Probably less sure than for that machine with hundreds of users...