It's not immediately clear to me whether this solves any part of the current problem. But on reflection, I believe I understand the motivation here. Big companies that use patents as a revenue stream (MSFT, IBM, etc.) typically bide their time and bring a patent lawsuit once a new company is established and there is blood to drain. It's the threat of such a lawsuit in the future that can negatively impact investment…
If you want to start a movement, you can't aim too high initially, or you just stall. The patent pledge in its current form is at least fairly easy to swallow. If it sticks, it will have the effect of making patent suits against competitors seem more dubious, which would in turn prepare people for more exacting versions. How far ultimately would you want to push it? I honestly don't know yet. Patents may have some ut…
Let me address your last sentence, though. Your statement presupposes a utilitarian moral system. That is, it assumes that a person's position is completely determined by which policy will result in the greatest growth in technology.
I've studied the history of patents as well, and I share your practical uncertainly over which policy inspires more growth. Patents may, in fact, grow certain types of technology faster while inhibiting growth in other areas. Since we need to weigh the harm caused by the lack of things that never existed against the benefits brought by things that do, it's probably impossible to do a quantitative analysis that is fair to both sides.
However, I and many others oppose patents on deontological grounds. That is, even if the existence of a patent monopoly produces some technological benefits as compared to a non-monopolistic system, we would choose freedom from monopoly.
John Carmack may have stated the essence of this position better than anyone since Jefferson [1]:
"The idea that I can be presented with a problem, set out to logically solve it with the tools at hand, and wind up with a program that could not be legally used because someone else followed the same logical steps some years ago and filed for a patent on it is horrifying." -- John Carmack
[1] "If nature has made any one thing less susceptible than all others of exclusive property, it is the action of the thinking power called an idea, which an individual may exclusively possess as long as he keeps it to himself; but the moment it is divulged, it forces itself into the possession of every one, and the receiver cannot dispossess himself of it. Its peculiar character, too, is that no one possesses the less, because every other possesses the whole of it. He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me." -- Thomas Jefferson