i will briefly answer just the second part of the question ( why do you think it's not necessary in todays world?), as i think ingrate did a decent job on the first part.
unfortunately, i think it IS necessary in today's world. the primary reason for that is the scale and complexity of human social structures that have developed. mass society seems completely dependent on the institutions that define and control it (and vice versa), with government playing a/the central role in that.
the push towards a single, homogeneous (in many ways at least) society/culture is a necessity for capitalism, government, religion, and even civilization itself - despite all the rhetoric about diversity etc. a world where humans lived in much smaller, voluntary, informal and often transient "groupings" (better term needed) would NOT necessarily require government.