Comment by gptgpp

Broadly speaking there does exist a defense of "innocent infringement." You can use that keyword to read about it more yourself.

IANAL but I believe it only reduces your damages in an infringement suit. It's considered your responsibility to check if something infringes on an existing patent. Yes, I know there are patents on absurd things like doubly linked lists, and the whole thing is a bit of a mess, seemingly created to give lawyers a job and present a barrier to people who can't afford to do patent discovery and all that.

As for it being absurd.... I don't know.

Would you prefer that companies never file patents, revealing their algorithms and mathematical solutions, so it never becomes public knowledge (and useable by everyone once the patent expires), and they just keep it indefinitely as trade secrets?

Because that's the alternative :(