Anyone and everyone gets nervous when people talk about tolls on infrastructure bottlenecks. This isn't a car bridge. There is no alternative route, at any price. Those using the lock would have no option but to pay. Such a monopoly in private hands will never be popular.

Tolls on interstate infrastructure have also traditionally been looked down upon. Charging people to move themselves or goods across state lines, even where arguably constitutional, rubs Americans the wrong way. Easing interstate commerce is a large part of why the federal government exists.