I agree that a lot of so-called "sample code" does more harm than good, but I wouldn't go as far as to say "Nothing is more deterimental..."

Just as teaching is, itself, a skill; so is producing worthwhile sample code.
To be of instructional value, the sample code needs to be written with the express purpose of illustration and instruction.
In most cases, code just ripped out of some other project will not meet this basic requirement!