I think its a coincidence. I'm playing a household where the IF's end up being the spouses of their real life friends. I've only had one that was evil (I'm playing 5 right now), Other traits were workaholic, snob, genius, schmoozer, natural cook, hydrophobic, evil, disciplined, eco-friendly, coward, born salesman, and couch potato. So some useful, some not, of course turning them human is great because I can then balance the "bad" traits with something good.
I find the IF's frustrating as toys with children because they keep the children from doing important things like homework. I like to micromanage my Sims and the IF's are my worst nightmare!!

But they make beautiful spouses and so I kept the dolls in the inventory until I had the potion ready and then they come out to play, and be turned into a real boy/girl.