Because a "right" has to mean more than "I think we should do things this way" when those who have the exclusive power to do things that way don't agree with you.
You see, that's exactly what a right is. When the gp said "Privacy is an inherent human right" he meant that it was important for all people (govt included) to respect that. The govt doesn't respect that though, and if you accept privacy as a right, the govt becomes an aggressor and in the wrong. The same thing for life and liberty. The govt can and has taken those things away, but that makes the govt wrong and illegitimate. You said "They're just ideas. Perhaps good, perhaps not, but still, no more than thoughts." Again, true. But while those in power take and take and take, the fact that those rights still exist and can be shown to arise naturally makes those in power wrong. Your response is mainly "who the fuck cares what you say your rights are? Those in power take what they want." This, unfortunately, is true, too. But one day we might be able to rid ourselves of those in power who control us. We might have the opportunity to create a new or smaller society and we'll need rules. Our current govt was conceived with those rights in mind, for the most part. They just missed with the checks and balances.
Rights are not something that will protect you. They won't keep you out of jail; it is up to us to defend our rights. They are a philosophical point that defines the boundaries between people. They're more than a nice thought, though - they are what we use to describe a moral society. But they won't keep you out of jail.
There are no "inherent human rights...they are simply grants supported by power.
Well, not really true. The inherent rights to your own life and liberty arise from the assumption that people own themselves. Of course, this is an assumption that we've made that has allowed democracy and freedom to flourish. You might not accept that assumption. You might start with the assumption that society has ownership of the people, in which case you'll likely end up with a communistic government. But we started with the assumption that we own ourselves, which makes sense because outside the context of a society, people are free to do as they please.
Now if we own ourselves we own our lives. No one can take that away unless we give it to them. Likewise, if we own ourselves we own our actions, and by extension, our labor. Suddenly the "inherent" rights of life, liberty, and property are starting to show up. Your assertion that "they are simply grants supported by power" is wrong. Sure, the govt can force us to do things. They can stick us in jail, they can beat us. But they don't own our life liberty and property. They are stealing it from us. This is not a legitimate power. It is not a power that an outside observer can support. It is a power that derives its strength from the mere fact that it is stronger than us. As soon as a stronger power comes along, the old govt will topple and will prove to be transient. A govt based on the assumption of individual sovereignty, however, will stand the test of time - even when temporarily taken over by a stronger power - because it is based on a simple assumption that people inherently want to believe.
Never trust an operating system.