The patent is the land, not the crop. The products that can be produced with the patent are the crops, with which it is impossible to have without the patent. Think of it this way, you spend years cracking a new invention. You bring it to market. You immediately go out of business because a larger company takes your invention and sells it at half the price you can because they don't need to recoup your R&D costs. Without patents you cannot protect against this circumstance.
Trade secrets don't protect against this because trade secrets don't protect against reverse-engineering whereas patents do. Patents are a temporary monopoly. Trade secrets can last indefinitely. Patents have a relatively short lifetime, though people do argue one still too-long for software.
I think this scenario is more realistic.
You don't need patents to build software but you need land for crops.