Well, I too don't see what the problem is with requiring/expecting passing cars to go completely into the oncoming lane when passing. They'd do so to pass a car, right?

The safest thing for everyone is to drive like a bicycle and a car are the same size. Imagine they take up the same square footage, and then place the cyclist inside that imaginary car-sized rectangle and don't encroach upon it at all so that he has the buffer space all around him.

But personally, I don't get bent out of shape if drivers pass closely: as long as they don't cause me to alter my path then my life hasn't changed one bit.