Banning has nothing to do with conversion. Nor does it have anything to do with how long you've been running on the network without getting caught. We ban affiliates for delivering fraudulent leads.
You want to use invalid iframes on our offers? You want to use a CL fake job or apartment scam? You want to fill out your own offers? Maybe incentivize campaigns that don't allow it. Go ahead, but know that you are basically playing russian roulette with your account. You might not get caught now, you might not get caught tomorrow, but you never know when that bullet will be in the right chamber and your account will get banned.
I don't know what specifically happened with 420's account as I can't match up handles to affiliate accounts, but my guess is that he was misrepresenting an offer (maybe with a fake job ad). Nothing that could be easily caught, but one day some pissed off surfer got angry enough to complain to the merchant and guess what? Shit flows downhill.