Hi pooka,
I don't do weight watchers, but I am familiar with it. I think the calories in/calories out concept is true, and you can probably still lose weight if you stay within your points.
I would guess that the problem with choosing less healthful choices (besides not getting your necessary nutrients) is that you'd end up having to eat a lot less since the less healthy stuff tends to be more points. Then you'd probably be starving in between meals and (I would probably) end up saying heck with the points!!!
Maybe a compromise between *mostly* healthy choices, then some treats? My sister has had an amazing weight loss following her 80-20 rule. 80% healthy stuff, and 20% whatever.
Best of luck to you!!!!!