Earlier quoted context omitted.
If you could build a cold fusion reactor (and let's say you get only one patent from it), wouldn't people be begging for you to build it? If you could turn your patent into VC funding, had proven it in the lab, and were actively seeking investors for it, then yes you deserve the patent. If you can't do any of those things, is the patent worth anything? Maybe it's cost prohibitive - maybe, in that instance it would be…
The problem is that no one would believe you. And since you don't have any IP protection, the second you showed off anything of real interest (to prove you could do it), they could simply steal the idea at that point.
The problem with this model is now, "how do you define "actively trying to commercialize?" Patent trolls would then just move to doing the bare minimum to qualify for this category. If we make it prohibitively expensive, however, we may eliminate some of the patent trolls.
Some ideas in this direction:
1) IP companies must notify any infringing company within 3 months of the infringing product's release. IP companies can't wait until something like the iPhone blows up to sue.
2) If a company wants to maintain a patent, it must either be a commercial product or be willing to license it for a reasonable fee. Some IP companies refuse to license at first, in order to drive up the price.
3) Every 3 years that you have the patent, you must show progress towards commerciality (commerciality remains to be defined in this thought experiment).
4) The patents for ideas, strategies, etc. should either be banned outright, or the lengths made much, much shorter. There's no reason that Amazon should still have a patent over "one-click" in 2010.
My problem with "no one would believe you" is that it remains purely hypothetical. Capitalism and the marketplace has proven time and time again to be the great equalizer. If you had a working cold fusion experiment that you could patent, why wouldn't they believe you if you could prove it in a laboratory setting?