True, but similar justifications could be made for any expanse of government power.
True, which is why as people of intelligence we must consider such arguments in depth rather than taking them at face value. Some degree of government is necessary otherwise you get chaos and anarchy which likely leads to tyranny in the long run. Too much government however leads to the people being controlled and freedoms being restricted. While similar justifications could be made for many government expansions, that doesn't mean those justifications are necessarily valid. We may come to different conclusions, but what matters more to me is that we use logic and reason to come to those conclusions.
It isn't the only source, but it is a large one. Since the government has the most power, (they probably wouldn't be in charge otherwise) it has the greatest ability to oppress the people, so it seems natural to concentrate one's efforts mainly on the government. For the same reasons, other oppressive forces will often concentrate their efforts on getting the government to do what they want. Take for instance corporations lobbying government for corporate welfare, land seizures for private use, etc. - libertarians oppose these things, but we aren't going to get them to stop lobbying for them by asking the corporations nicely. It's the government that gives them these things, so we need to get the government to say "no" before anything else can be done.
Libertarian views of property start with self-ownership, so slavery is abhorrent to libertarians.
Most libertarians would agree to some degree of law involving copyright. That degree varies by individual though.
One's emotions, hopes, fears, dreams, and ambitions are part of one's self, so under the doctrine of self-ownership they belong the person they came from.