This is badly misguided. It is true that design is a series of trade offs. At a certain point adding an extra safety check will not be worth the cost, whether that cost is in terms of dollars, complexity of the system, or something else undesirable.

However, there is absolutely no reason to assume that different approaches will arrive at the same trade offs. Of course a software pilot has cost/benefit trade offs, but they could potentially be more favorable trade offs than you get using a human pilot. The entire point of improving technology is that the balance of trade offs gets more favorable.