Governments support IP rights because: 1) the idea that creators have a right to control their works is more popular than the idea that the public has certain rights to access "culture"; 2) industries dependent on IP create jobs.
A senator supports the MPAA companies versus downloaders because he can easily see that the MPAA companies are a source of a large number of jobs. It's as simple as that.
But it's the control over derivative works (http://en.wikipedia.org/wiki/Derivative_work) that copyright gives you that's more obviously suppressive. All of the uses of Mona Lisa would be derivative, if Da Vinci's estate still owned the "intellectual property". All of the uses of Grant Wood's "American Gothic" would be derivative.
Yes, not all "derivative works" are worth it, but neither are most "original" works. 99% of everything is crap.
Copyright law is also used to suppress anything that the Rightsholder doesn't like: http://arstechnica.com/tech-policy/2013/03/gopro-can-fall-fr..., http://www.dailydot.com/business/dentist-bad-yelp-reviews-co... and many others.
This may indeed be an abuse of copyright law (copyfraud) but the laws are apparently intentionally written to allow this sort of thing. The practice is to not prosecute improper DMCA takedown notices, for example: http://www.techdirt.com/blog/?tag=copyfraud
So, yes, copyright per se doesn't tend to stifle free speech, but the concept of "intellectual property" gets used to get laws like DMCA passed, which are then promptly abused to censor people and their ideas. Moreover, the practice of lengthening copyright terms towards infinity keeps ideas out of the public domain, causing derivative works to not appear.
One more thing: Mickey Mouse Meets the Air Pirates. http://en.wikipedia.org/wiki/Air_Pirates If that ain't censorship, I don't know what is.
Neither of the examples you give really support that.
GoPro was about trademarks (and was hopeless anyway - it's not really the fault of trademark laws that someone can send a nastygram that's completely without legal merit, using 'trademark violation' as a scary magic word).
The dentist one was only worded in terms of copyright so that the dentist could use DMCA takedown notices. You could abolish copyright altogether, and that wouldn't stop a dodgy dentist putting a clause into their patient contract saying 'you can't post bad reviews' and suing people who do.
(Obviously it's bad that the DMCA is so easy to abuse, and the DMCA's flaws are well documented on hn - the point is, they're flaws in the DMCA, not in the concept of copyright).
Any particular instance of DMCA-based speech suppression is probably arguable. "Oh, that's just some crank getting riled up." You have to look at the DMCA as a system. The DMCA encourages notice and takedown, not notice and notice. The bias in copyright law as a whole is towards the rightsholder, so copyright law becomes an easy tool for abuse.
I do? I was approaching this thread as being about the correctness of IP rights as a concept. Again, I'm not disputing the defects of the DMCA, only the use of DMCA abuse to imply that the whole concept of copyright is inherently flawed. (As it happens, I don't even live in the US, so the DMCA doesn't apply to me).
> The bias in copyright law as a whole is towards the rightsholder
In its current US (and EU) implementations, sure. But unless you're saying the existence of copyright as a property right itself is the bias (in which case 'unbiased copyright law' would be an oxymoron), that's an implementation issue.