It isn't well argued, but the point is that if you have two chip designers/ISA shops in the world, both may make the same mistake. If the ISA is open, you (hope

It isn't well argued, but the point is that if you have two chip designers/ISA shops in the world, both may make the same mistake. If the ISA is open, you (hopefully) have a hundred, and not all will fool themselves the same way. Also, if you do come up with a better way, you've a much greater chance of persuading someone to implement it.