They should have reasonable length. Coming up with an idea doesn't forbid others to come up with same one, and tendency of that happening increases with appropriate developments. Thus many genius methods become a self-evident norm, not only because we have (if we do) an example.
Patents should become obsolete under certain conditions, like current topic ("everyone" does 3d printing these days, and such ideas doesn't require being a costly educated specialist anymore) and their huge lifetime is obsolete long ago, with increasing speeds of communication compared to when they first appeared.
There's a difference between protecting the inventor and creating a cash cow, which in turn is bought by someone anyway.