Ah! How sad it is to be so easily disappointed! 
Given that other moderators have explained our policy in this matter, I don’t think I need to belabor this further. I did say “virtually,” indicating that a case like you mention is relatively rare. In addition, if the rule violation was in fact inadvertent and your friend didn’t have other infractions, they can request reinstatement.
No doubt few if any of our spammers read the rules either, and we ban them without mercy. But I’m sure the rules would make no difference to them.