With their padding and other equipment, goalies are at a distinct disadvantage when they leave the crease. It would be silly to treat them the same as a regular skater just because they leave the confines of their crease. Being protected from getting run isn't an advantage they have over other players; it's just a rule to protect them and help mitigate the disadvantage they're at due to their equipment.
I'd ban goalies from leaving the crease/trapezoid before I make them fair game. The latter would just be terrible.
I just want to make it clear that I am not disputing anything you guys are saying. All of the things you mentioned are why the crease, and the double standard it represents wrt the protection it provides, exists. To extend this protection beyond the crease, where goaltenders are no longer just tending the goal, is unfair in my eyes.
To me, a goalie is the player sitting in the crease blocking the net. A goalie coming out of the crease to play the puck is a defenseman, and if he wants to do that, he should do so at the risk of getting hit just like any other defenseman. If a goalie doesn't have time to swiftly retrieve and move a puck before getting hit because his equipment affects his mobility too much, he should simply stay in the crease.
I'll admit that this is all coming from a guy who has played as a forward throughout my hockey "career". Nothing more frustrating than a goalie swinging out of the crease to block you on a forecheck and knowing that you have to let up or change direction to avoid him, even though they put themselves in your path. Stay in the crease. Very simple.