Human nature and society hasn't changed since then. Hell, it hasn't changed since wide spread written history. Go read ancient Greco-Roman graffiti. We are not fundamentally different than our ancestors, and it is the height of arrogance to pretend we are the enlightened peak so far above them.
The reasons for Marx's statements and the reasons the founders wrote the 2nd amendment have not changed, and technology has not changed sufficiently to invalidate that.