Copyright is an absolute cancer on society.

No, it isn't. The original intent of copyrights and patents both have just be subverted over time until they became their current form.

The idea of having someone have a temporary monopoly on a thing for a limited period of time completely makes sense (as long as you're under capitalism). Inventions and creative works take investment to produce, and those making that investment should see a payback on it.

However, over time, corporations have lobbied to make a temporary monopoly into a near permanent one. The public domain (until very recently) just didn't grow at all because of this influence. That's what's wrong here.

As per usual, the real bone to pick is with capitalism and regulatory capture. I think it's reasonable to say that, for instance, the Beatles operating under capitalism ought to have been paid for the works that they created. However, at some point, enough is enough.