The principle applies only to people who use alts. The purpose of alts is to avoid bans, so why would anyone exhibit ban-worthy behavior on an alt account? They're not going to change who they are because of a silly little ban, but, generally speaking, they're going to be a tad more cautious on an alt. Then again, if a ninja has it out for a user and figures out they're using an alt, they could get banned for saying literally anything.
*sigh* I'm not saying everyone who has alts is toxic, but the prime purpose of alts is to have a get-out-of-jail-free card. They don't care what happens, because now they know they're invincible. If anything, they were more cautious on their main.
While i do agree that an alt is a get out fo jail card, it certainly isn't invincible. An alt is capable of getting banned just as any other account is. If a person gets banned on their main, then a day later does the same stuff on their alt, then the alt gets banned too. It might not be a full, 7-day ban, but a 6-day ban is close enough to still be a punishment.
Even for severe cases, like people who harass other users with like 5 alts, the ninjas can just perma ban each alt. Of course, ninja justice isn't perfect, but it's what we have to work with.