Patents are a bargain with society: I, the inventor, will publish the details of my invention, instead of keeping it locked away forever as a trade secret. In return, you, the government, will grant me a limited monopoly on the invention.
But if the patent's teachings aren't even remotely necessary or helpful to those who implement my invention in the future, what exactly is society getting in exchange for the monopoly grant?
IMO, patents shouldn't be granted on anything that wouldn't otherwise be a candidate for trade secret protection. "Slide to unlock" certainly would never meet that bar. There is a 0% chance that anyone who is infringing on this patent needed to read it first.
You're making sense in general, but the other justification for patents besides encouraging disclosure of details would be encouraging exploration of a wide range of options. For example: I, the inventor, will experiment with thousands of materials to find the one most suitable as a lightbulb filament. In return, you, the government, will grant me a limited monopoly on use of that material as a lightbulb filament. Once I release a lightbulb with a bamboo filament my invention is trivial to reimplement, but that doesn't mean the patent isn't contributing anything useful.
Now in this case, the analogy would be I, Apple Computer, will experiment with thousands of touchscreen UIs to find the one most suitable for unlocking the device, and you, the government, will grant me a 20 year monopoly on whatever I come up with. I think the sane response is, "eh, no deal." We're just not getting enough out of the bargain. But "easy to reimplement once explained" isn't the problem there -- "easy to implement in the first place" or "no additional incentive required to encourage innovation" is.
The light bulb example isn't adequately addressed by my original argument, but I have another one up my sleeve. Namely: If it's likely to the point of being almost certain that someone else will soon come up with the same solution, it shouldn't be patentable.
If inventors are to be rewarded by monopoly grants, it should be for doing genuinely challenging, innovative research, not for winning a foot race to the patent office, as happened with popular technologies like the telephone, or for trying random stuff until you hit the lottery, like Edison did with the light bulb. We, the public, would not have had to wait much longer for electric lighting if patent protection had been unavailable. We didn't get anything special in return for our monopoly grant to Edison.
An appropriate quote that I saved from an earlier HN thread: "It has always appalled me that really bright scientists almost all work in the most competitive fields, the ones in which they are making the least difference. In other words, if they were hit by a truck, the same discovery would be made by somebody else about 10 minutes later." -Aubrey de Grey
You can't patent an idea, you can only patent an implementation of it. E.g., I can't patent a flying carpet until I actually know how to make it and prove that I can (by making it or being very specific in technical instructions on how to make it).
An patent is obvious if you can explain the idea, i.e. what you want the machine to do, to a graduate engineer/scientist, and have him implement it. As for the famous doubly-linked list patent: if I tell a programmer: "I have a number of items {A, B, C, D, E}, and sometimes I need to access them in the [A -> B -> C -> D -> E] sequence, and othertimes I need to access them in the [B -> C -> E -> A -> D] sequence. Make an efficient/working implementation of it!", then any programmer could come up with the doubly-linked list implementation. Ergo, it is obvious.
Many things are easy to implement but are difficult to conceptualize.