Originally theymos' quote was referring to that, for example, if you want to express your political ideas and you don't want to do it with your account.
I wasn't around in 2012, but I guess farming accounts for selling or signatures wasn't a thing back then.
I don't remember anyone getting caught with two or more undeclared alts and not breaking the rules in some way.
"Getting caught" implies you did something bad. If I find your alt (or any other personal information about you), and you're not doing anything wrong, I wouldn't expose you.