This would certainly stops patent trolls, and avoid making people suspicious when you claim "protective patents" as you describe.
Personally I believe that we should simply abolish software patents: Innovation in the software world seems to thrive without a patent process too, and in fact the patent process seems to be a major hurdle for small players to enter an existing market here.
a) it's about things that should have been actually used, where a patent is about concepts
b) scope of the idea is not clearly defined and so could be argued with, when a real patent definition for general public use would prohibit that.
And that's excatly the point for IBM to issue protective patents, I think.