Well, I don't know about you, but I put my foot on the ground when I come to a stop . I've lost balance on a stopped bike with rear panniers. Even with my feet on the ground and a firm grip on the bike, once the weight on the rear has tipped more than a couple inches to the side, it just pulls the bike down, dragging the front wheel with it. I haven't ridden with just front panniers, but they prevent that sort of thing from happening by weighing down the front of the bike. Given the location, I don't see front panniers making balance any worse than rear ones do, and likely better.

Don't get me wrong - from a practical standpoint, I'm with you. I just don't think that the argument that weight is more stable on the rear rack is convincing.