The Founders believe the items in the Bill of Rights were God given natural rights.. as in ones that are always present, always there.. not to say that the right may not be prohibited.. Governments at the time were well known to refuse you these natural rights-- which is part of why we rebelled against England. But no matter what, the natural rights still exist, even if they are denied by a government or individual.
The Founders knew that you didn't need a document to give you these certain, inalienable rights.. no document can give you what you were born with anyways; but a document was needed to REAFFIRM that they were in fact natural, inalienable, and not to be infringed upon.
What you have to understand is that many liberal thought-aligned Americans, so-called Progressives do not believe this to be true. They believe that we can take care of each other, and that a good strong government can protect you, that you do not have, nor do you need a natural right of self-defense. And even if you have it, it is not necessary. This is where conservatives, tea party activists, libertarians, and others feel that the progressives are wrong.
What is sad is that they truly and honestly think they are doing what is right and for the good of the country and its people.. but history and example after example proves this to be a fallacy.