Curiously enough, some of the points made by 'anon' in the parent post here used to be part of some patent law systems in really ancient times (like 16th-18th centuries), but they were one by one abandoned, by court decisions or legislative amendments:
>> 1) Patent times are FAR too long in many cases and should not be renewable.
An early example of a time limit, fixed in 1623 in England, was 14 years from a really early time-point when patent grant took place -- which used to be almost immediately on application (compared with today's long process).
Current patents are 20 years from the filing date. This was extended in the 90s, up from 17 years, not sure why. But 20 years isn't much longer than 14 years. I expect someone was thinking of Copyright lengths.