Since I'll know a fair price of the vehicle before I run across that, I can determine if it is a "ripe off" or a fair market price, with far less hassle/wasted time. I'd always buy from a no haggle dealership if the price was competitive (and my last vehicle purchase was exactly that, it was +-$1K from normal price based on vehicle loan records).
You also have it backwards. The current system of "MSRP as guideline" and you have to negotiate to find the real price makes it more difficult to compare prices between cars and automakers (unless you relish negotiating the prices of 4 competing cars simultaneously at 4 different dealers). The current system is set up precisely to not be price transparent.
Just like now, but dealerships add a whole layer you have to figure out by determining likely "discounts" between different brand's dealerships.
If the manufacturer could charge more they'd already be doing so, the dealership doesn't actually dictate the prices, they get told the price and are expected to negotiate up then keep the difference.