It's a fine regulation. Anyone who cares can visually evaluate an individual package prior to purchasing it. With no window, it'd be a crapshoot to do things like price shop, because who knows what is in that completely covered package.
But it is still the case that the regulation isn't as silly as you made it out to be, it's not exactly expensive for producers to leave a clear window in their clear plastic packaging and it has some benefit to consumers.
Maybe it's related to this discussion, but I was comparing packages of bacon using the window just today...
