Many voters, thereby, probably did not even realize that this other aspect was a consequence; those that did may have not cared enough to think about it (as it doesn't affect them personally), and those that cared may have decided "on the balance, in this flawed democratic system where I have to vote on this as a single unit, I think the result is better despite this consequence" (I often wish I could vote "I agree with these specific diff hunks" as opposed to "I agree with this changeset" ;P).
(I say this not to defend the law, but as a way to try to explain why 81% of the people in my state apparently voted for it; when I saw the number I was thereby depressed, but not really surprised: human trafficking "sounds bad". Also, the official "CON" argument blurb was "I provide erotic services, and this (might) incorrectly label my son", which probably turned off a lot of conservative voters in addition to being an argument many would call "far fetched", even if it totally ends up happening.)