Moisture control wasn't a big problem in mild climates before the 70's. Houses were so leaky that air infiltration took care of any buildup. The energy codes changed all that.
In cold climates, moisture control has always been a problem. Human occupancy generates moisture from transpiration, cooking, bathing, etc. This moisture needs to be removed from the living space, or it will condense on the first cold surface it finds. It may be a cold water pipe, a window frame, or the building sheathing. If that surface is within a wall, rot and mold will follow, and exterior paint will peel.
To do the job right in a cold climate, the vapor barrier should be on the inside of the walls, and completely sealed around electrical outlets, light fixtures and such. The tightness should be verified with a pressure test. The outside wall surface should keep the weather out, but be able to "breathe" so that any moisture that does get past the primary barrier can escape.
The reason that you see so many varying opinions on this problem is that there is no one-size-fits-all solution to moisture control. There are about a zillion books on moisture control in buildings at amazon.com. Here is one at random:
Moisture Control Handbook: Principles and Practices for Residential and Small Commercial Buildings