> You could spend 20 years building something and have it stolen by a huge company with no means to recoup your costs. Removing patents would immediately benefit the biggest players, entrenching existing monopolies.
But why is the big company stealing it? Currently, it makes sense to steal it because the patent protections make it seem as if the idea itself is valuable (and can be a private property not commons). But in the world without the patents, what is valuable is the physical implementation, or rather, the coupling of both.
It has been pointed out that you have many cases in free market economy with a similar problem. iPhone, for example, has very little innovation in it, it's just an idea executed well, based on past things like Palm Pilot for example.
It seems to me, to have fair patents, you need to assume that value of everything can be broken to additive pieces - value of this idea, that idea, and then the value of the materials and energy from which it is built. But this is really hard, because things have value that also comes from combining these things. (In general, this is a problem with free market with respect to labor too, because you cannot really meaningfully determine what contribution of different types of labor is more valuable for the product to arise, but at the same time, the people need to be remunerated for the labor somehow.)
On the other hand, in the world without patents, we assume that value of everything can be broken to little pieces (not so valuable by themselves) that are added by individuals in small amounts. So if all innovation is in the commons, no need to toil for 20 years to invent something. You build a little piece, add it to the pile, and everybody benefits because at the end of the day, you take lot more from the pile than you put in.