Go anywhere in the world, at any time in history, and you will find people (in the absence of tyranny or insanity) making the same agreements: to respect each other's rights to life, expression and self defense.
Note: we must exclude tyranny on the grounds that inalienable does not mean inviolable, and we must exclude the insane on the grounds that this is a sociological concept.
As a result of the need for self preservation.
The idea is that these rights emerge as universal agreements in human society as a result of the need for self preservation of our species. When the founders wrote "endowed by their Creator" the point was not to qualify their existence on that of a deity but to qualify their existence on mankind.
As rights are a social construct, they can only be understood through a sociological perspective. The concept of rights to an individual in isolation, acting according only to their own whim, is meaningless.
Those are agreements are not universal over the past. For example, certain ancient Mesopotamian societies. In those, certain children who were born under certain conditions were destined to be sacrificed. There was no universal right to life, and if you were to ask anyone in that society whether there was a universal right to life they would say no. Because the sacrifice of those specific children was key to the continuation of their civilization. This was seen as an honour for the children being sacrificed, as they would go on to join the gods in the afterlife. You may say that we can dismiss this as insane, but insanity is completely subjective, and based upon our own (i.e. the 21st century wests) sociological lens. As you say, it's a sociological concept, and that means that it can't transcend society.
Perhaps more importantly, there is no guarantee that these rights will continue to be universal in the future. In 500 years, should we replace biological bodies with easily replaceable robotic ones, rights to self defense might become obsolete as we can simply manufacture more body parts. The 'universally agreed upon' rights you mention may arise out of human nature but human nature has changed in the past and will continue to change in the future.
The right to bear arms is the only way to realize the right to self defense for the masses. In this, it becomes a natural right. I derive the natural right to arms from self defense, not property.
Disagree. In a society without guns, then bearing one
is not the only way to be able to defend oneself. Likewise, in a society with magic wands, bearing a gun is not the only way to realize the right of self defense. The ability to bear arms is but one possible way to ensure the right to self preservation. That does not mean that you can equate the two.
rights are not collective, because the people do not get together and decide what rights the people of the group will have.
Just because people don't get together and decide doesn't mean that rights are not collective.
Rights are contingent on interactions between multiple parties, and it is in how those parties interact that the framework of rights is built. You can't have rights without those interactions.
Those interactions may arise from human nature itself (human tendencies to form groups, to bond, to protect each other etc) rather than being specifically decided upon, but they are still collective.
God is the author of human nature, even though you reject him.
Baseless. Anthropologists can demonstrate how the author of human nature is evolution and genetics. Can you demonstrate otherwise?