I have mixed opinions on this topic.
Borders are a man-made thing that has no real worth or value aside from that we are giving it. It's the same as is the case with things like religion or money, these topics cause problems because we are giving them meaning.
They exist. Yes they are man made but if people are directed primarily by emotions and feelings and lack most knowledge of critical thinking then such things are needed. People can be a fan of anarchy, and I do know what the word really means. Yet while the population suffers from the poor education and an interest in NOT teaching critical thinking then anarchy is something that cannot work. Anarchy requires people be self responsible, and be able to reason, and choose for themselves (NOT OTHERS). If you want to remove borders then the first thing to do is fix the global education. Teach people to think for themselves rather than teaching them to believe what they are told. They can consider what they are told, but they need to ultimately do their own thinking.
We are not there.
Borders matter to a nation just like the door does to your house. There is not really a difference other than scale. They both serve the same purposes.
As far as man-made. So what? Should we move back into caves and use stones as our only tools? Everything else is man made.
If you would give me good reasons for moving back into a cave, I would consider it.
I agree with most of the things you are saying here. Proper education and knowledge are important. I also think that teaching these to a population is much less complicated and costly than having borders and keeping them secure and in check.