so I wouldn't worry about it too much.

Neither would I. In fact, since I don't run this site, I wouldn't worry about it at all :)

That said, it's all a matter of cost vs. benefit. The probability of any damage actually coming from copyright infringement is next to none, worst case you get a cease and desist letter (and even that has a very low probability).

As for offensive content and falling trees, you never know who might walk along after the tree has fallen. It would reflect poorly on Perlmonks, but the odds are slim and definately wouldn't outweigh the benefits.

it's far from trivial to generate random strings that look like a language but isn't.

I've never done it, so I can't say for certain, but in theory it would appear to be remarkably easy. A simple example could be to just rot13 an english post, add/subtract a specific amount of padding from each word, and vary the punctuation slightly. More complex examples could be done in under an hour as well. Granted, I doubt it would ever cause a problem, but it certainly doesn't appear difficult.