Where do you get inalienable from? Whatever rights to property you enjoy are granted by the consensus of the people around you. If you piss them off enough, they'll revoke those rights.
I wonder if your question is facetious or ignorant, but I will answer you as though it is earnest: I get it from great thinkers such as John Locke, George Mason, and Thomas Jefferson. To the extent that you support any kind of civilizational progress, you have these thinkers and their ideas to thank.