Copyright has been extended over twenty times, the last time so Mickey Mouse would not go into the public domain.
The same thing is going to happen to patents.
There is no difference between eternal copyright/patent and extending the term every time one is about to expire.
When you have the Patent Office granting patents on double clicking an icon to make a purchase, the abuse has reached an apex and it is time for the party to be over.
That's just throwing out the baby with the bath water, to repeat a timeworn cliche. The answer is to reform the system, not to destroy it.
Twenty distinct times? I would be very surprised.
Until the 1976 Copyright Act, copyrights were 28 initial, renewable for an additional 28. I believe the 28+28 was an extension of 28+14. I don't know how many times copyright had been extended to reach the 28+14 standard, but I'd be surprised if it was more than half a dozen.
The 1976 Copyright Act extended copyrights to life+50 for authored works, or 75 years for works-for-hire; the Bono Perpetual Copyright act amended those limits to life+70 and 95 years, respectively.
What other copyright extensions have there been?