The bad publicity associated with suing "little guys" tends to prevent big companies from suing.

For each instance where this is true, there are an equal number of instances where the "little guy" is strong-armed by the big guys. In any event, the point of the original post remains true - the cost of litigating patent validity between parties is high; it makes more sense to offload those costs to the PTO which has the internal mechanisms in place to make review more efficient.

If the costs to litigate validity are significantly reduced, the blackmailing that occurs on both sides of the patent would be reduced. Obviously, the PTO would only answer the question of validity, courts would still decide infringement issues.