Oh, it's not just illegal in many countries, but it's also NOT suitable for Google AdSense. You know the AdSense rules are pretty strict (and I would say -- moral).
I do agree -- let sleeping dogs lay in this case!
Btw, it's a very wise decision a person to stay far away from this kind of online activity. Better safe, than sorry, you know.
(I just imagined something like recipes website with unique (i.e. not copy-pasted) content, and I was like: "Wow! It's a golden opportunity!"). At least now it's clear.
(One good psychologist and comparatively famous in Europe usually answered to the boys, who wondered if they should say to the pretty attractive girls they like them: "Yes, you should do it. If the beauty refuse to be with you, AT LEAST YOU WILL BE CLEAT ABOUT IT!"
And now I use the same modus: "Better clear than nothing."