Even if we are to take that for granted, which I don't think we should with software patents because many companies and developers could invent the same feature

Even if we are to take that for granted, which I don't think we should with software patents because many companies and developers could invent the same feature in parallel independent of each other, and I don't think it's fair for just one to get a 20 year monopoly, I do still think that the longevity of the patent should be granted based on the difficulty to implement of the invention. Something as easy to implement as a read-receipt shouldn't receive a 20 year monopoly, because there are like a million other features like it that could also receive a 20 year patent monopoly, and then we get into this situation where rent-seeking even from companies that didn't invent the thing in the first place, get to sue others for "copying them" (but again, could have been independently developed). If there are a million patents on stuff like read-receipt it also doesn't help innovation, but hurts it. The big companies will acquire as many of those patents as possible and then crush the newcomers. The first reason this doesn't happen as often as it should based on how many useless patents are out there, is because most companies aren't assholes and don't enforce their patents against others. The second reason is because most companies don't waste time looking at all the other companies' code and patents to see if they can sue them for infringement. Only a certain class of companies do that. The third reason is that among the big established players that somehow avoided getting crushed in the early days because enforcement of patent infringement couldn't be perfect, there is a certain "mutual destruction agreement", so even if they infringe on ton of each other's patents, they can't practically sue each other, because it would be pointless, most of the time. However, this mutual destruction agreement was never supposed to be part of the patent system, it's just the natural outcome of a broken system that grants patents for everything. I think it was Bloomberg that had an article once saying that there are like 250,000 patents for building a smartphone. If everyone wanted even 1 cent for each of those patents, and the enforcement would be 100% perfect, the smartphone would never even be invented (as an aggregation of all of those patents).