It's perfectly reasonable to leave a job after six months. Hell, it's reasonable to leave after the first day if you can see that life is going to suck.

But in real life, the next person to interview you will want to know why you left so soon. If your answer is along the lines of "I was being rotated through different departments for training and I didn't like the first rotation" that person will probably not hire you, expecting that you'll leave the first time things don't go your way.

You are correct that an applicant can make the wrong decision, but that's not what matters. What matters is how he responds to making that decision.