Not sure what the morality of taking bump vouchers has to do with OP; it appears that they are asking if taking them is against United's rules and regulations, not what John Doe thinks of airlines banning people from their FF programs and what criteria justifies one's banning from an airline.

Anyhow, the Rolling Stone article details that "Lucky" was attempting to gather as many vouchers as possible, often in questionable methods -- submitting large amounts of bogus complaints, exploiting computer security holes, etc. then proceeded to brag about it far and wide about how "The people running the airlines are all a bunch of idiots" -- the same "idiots" who revoked all of his vouchers and banned "Lucky" from MileagePlus.

-LPDAL