This is already pretty well-written. As well as correcting general errors, I'm also going to offer more suitable words or phrases.

The Hypocrisy Underlying the Concept of Being a "Citizen of the World"

Anyone who is learning a foreign language naturally tends to develop respect for other cultures. Maybe as they learns more about other countries and becomes fluent in several languages, it would be easier to consider themselves as a "citizens of the world". I'm all for world peace and the positive sides of international exchange. However, I do have a problem with those people who calls or would like to think themselves as a citizen of the world or an internationalist.

I swapped to the plural form to avoid the messy he/she text. The addition of do is to emphasise contrast against the previous sentence.

I admit there are many people who do have deep connections with other countries; some may have grown up in a country which their parents had immigrated to, and others may have spent a number of years outside their home countries. However, that doesn't make you a citizen of the world, as if you know and have experienced everything in the world, because it's impossible for anyone to be part of every single cultures and all country in the world. Sometimes it appalls me to meet someone who can unthoughtfully thoughtlessly say that. One might say, "Oh I grew up in this country and later moved to that country and I am now working here. I have many friends all over the world. I'd like to think I'm a citizen of the world." NO, you are merely a citizen of the country(s) your passport(s) states.

I changed the wording a little to fit the register. Suddenly you began to speak in a very casual way.

Belonging to a certain nationality does not mean it's OK to treat foreign people unfairly, of course. It's completely wrong to exploit developing countries, drop bombs on innocent civilians in war, leave underprivileged children starving, and so on. What I'd like to highlight is their refusal to admit we all have personal favors to the countries we are deeply connected with, no matter how much you hope to treat all people "equally." Maybe you didn't choose to have those connections, but you can't get away from them in spite of how mixed or not unmixed your ethnic backgrounds are, because that shows how you've ended up where you are now.

It's a little difficult to understand what the topic of the paragraph is here. You began talking in general, but then quickly moved back to talking about certain people. I'm not sure how to interpret the last sentence... it seems there's something else I should know to fully get your meaning.

As far as I'm concerned, citizenship is not something you can pick or "put on" or "take off" depending on your at will, as if it were a jacket.

The phrase "citizen of the world" disrespects the individual uniqueness of history that each country has gone through, and instead views the world as a place everyone can fathom by calling themselves a citizen, which thereby putting the world in a universal box. This over-simplified notion that the world is understandable because "Everyone is the same after all." is just a pure arrogance and it actually shows speaks volumes about how ignorant you truly are, no matter how many countries you've been to or how many languages you speak.

Good writing - I'm surprised this hasn't sparked a discussion.

Hello *Peachey* (my apologies for the typo in my comment)

As for the part that wasn't clear,

I meant to say that I did side with the humanitarian way of thinking that people should treat their own countries like others, but it was unfortunately impossible to actually act accordingly all the time because when push comes to shove, more often than not, people would choose the countries where they hope to belong. That's the dilemmatic part of belonging to specific countries. Admittedly it has a point in saying we all belong to the human race, "ask not whom the bell tolls", but saying belonging to all countries means not belonging to any country at all. 

I'm very curious about your take on it. It's be great if you could share your thoughts.