I think it is generally fine to consider the things we do playing with stuff—I consider myself very lucky to enjoy playing with computers as they’ll let you have careers in that.

But, for example, if I say that this site is a bunch of people playing at being engineers, in most contexts (maybe other than this thread) I’d expect to get some pretty annoyed responses.

Firstly, because there’s a difference between saying we’re playing with a problem, and saying we’re playing at being something.

Secondly, because it is great to be self-effacing, but less so to be others-effacing.