I think the idea of no borders and being citizens of the world, all of us, is a great idea. But it requires that we all (billions of us) agree to the same set of rules and respect for other people...and punishment when people violate the rules. What does that sound like? Government.
I don't see those who claimed lands as bad, evil people trying to rule others. Who claimed lands needed to have security mechanisms to defend their land, what means they needed to be intelligent persons, able to create things and solve problems.
... if they were unhappy they could li[v]e by themselves on the forests, mountains or to find another land.
If a person takes enough land to live and does not kill those who settle nearby then all is good. But that is not the reality today. Some people own enough land for thousands of people, and many others own none.
Living in the forests or going to new places is not an easy option. You need to buy paper to not be harassed by police, you need to be careful of local customs to not get attacked for offending somebody's belief, etc.
No matter how good your intention may be, i.e., just to settle harmlessly somewhere and live your life, in most places you cannot do that because a) government employees will attack you and b) wealthy people who see you as a threat to their power will attack you and c) poor uneducated people who see you as a threat to their bliss will attack you.
Government is still necessary until education makes it not.
I was talking about the middle ages and before. The beginning of our society. Today is similar on some aspects, but the humanity evolved, technology evolved, everything evolved...
We can't live in 2017 like nomads and forest-bush people.