I disagree. In an autonomous system, more sensors is almost always better, provided you have enough computing power to process the data. Having two sensors that disagree gives you much more information than if you had a single sensor with a malfunction. In the first case, you know there's some kind of fault and can take steps to fix it. In the second, you're running off bad data and who knows what could happen.

Three sensors are better than two—it's a common setup in flight control systems to have three identical computers running all calculations, and the majority opinion is taken as truth.