The Benefits of Patriotism
When people love the country where they grew up and they know about most, they prefer living there and helping it most, which keeps a balance between world's resources and populations, thus equality among Earth inhabitants by avoiding the centralization of one country/few countries everyone wants to migrate to while deserting their home countries — as in internal migration, or urban centralization, where a single city gets the lion's share of attention, services, and population.
DECENTRALIZATION is achieved by keeping people from flocking to the centralized countries, while encouraging those living there to live elsewhere, to create a fair power-balanced multipolar world.
Poor/unsafe/oppressive states should satisfy the basic needs of citizens first, to make life bearable there: their well-being, security and freedom, the lack of which makes many desert their country. Citizens' rights should be properly protected from violation by one another, by those in power, and by other countries.
Meanwhile, rich countries, whose citizens have a surplus of resources and more freedom of mobility between world's countries, should encourage citizens to explore, help or even inhabit other parts of the world. This helps achieve world balance, as well as giving citizens a uniqueness/self-actualization they miss in their overly-rich technologically-advanced countries, that don't benefit properly from their "skills" that another poor country could desperately need (like a company laying off gifted employees who can still be useful elsewhere). First world citizens should generally have a "broader patriotism" (acting more like Citizens of the World) than that of poor citizens stuck in third world countries. Their patriotism toward their home country is expressed by progressing further at home, while representing it abroad as good ambassadors sharing its experience and models of success with others. Patriotism is not absolute; it's derived from mutual interest wherever, whenever.
Some argue against patriotism saying that the centralization of some privileged countries is not harmful:
The natural resources a certain region has are better handled by the people living nearby, to save the cost of "transport, import, maintenance & adjustment" of commodities and humans, who must apply, travel and adjust to the host country they should first know, like and benefit from.
Any country's priority is to achieve SELF-SUFFICIENCY first, whenever possible, for saving the above costs, as well as avoiding the monopoly of big countries. Self-sufficiency is achieved in many ways:
Resources are better managed by the people who lived long in a certain place, since they usually know better about it. Meanwhile, importing foreign experts/workers is good only when a certain expertise/labor force is lacking at home (just as we import foreign goods, as long as the "human imports" are not more harmful than useful). The bulk of useful knowledge someone has (from work/education/reading/experience) affects them & the place where they live:
If your knowledge is of a universal type, equally useful and valued anywhere; then it makes no difference where you live as long as you enjoy your life.
It's better when each country finds its own niche in world order, where it can present to other countries something unique unfound elsewhere, natural or acquired. No country is 100% self-sufficient, however it aspires to be, that it needs others to be complete, not to compete with. Patriotism creates a more diverse world than a homogeneous one (that some wrongly charge patriotism with), where every nation knows who and where it is, before moving forward or outward.
Loving a place/time/person makes one automatically love, learn, cherish, and improve the special qualities about it/them. Patriotism instinctively guides citizens to discover their natural and cultural specialties: their own resources, traditions, industries, and identity that has existed for ages. They won't imitate or copy another country blindly. They mindfully will, only to add foreign elements to serve the local ones, when no home equivalent is found.
Specialization is personally useful too. When one is happy/successful/famous in a different/difficult environment, it makes outsiders more curious about, respectful of, and willing to benefit from them and their unique experiences. One can cooperate more with others, when one has something different to offer.
People whose origins belong to a certain place, or whose past memories took place there, are more emotionally attached to it, which motivates them to devote more time & energy to it, than those who had neither memories nor origins there. They can endure many hardships their country faces, willing to sacrifice some of their own self-interest for the public interest, and temporary gains for future ones. Examples:
Every relationship is based on "mutual interest." A country needs its citizens as citizens need their county; and each is affected by the changes happening to the other: physical, financial, social, political, etc.
Like a mother, a nation gives more privileges, e.g. citizenship, to inhabitants who are more emotionally bonded to it (patriotic), for growing up/living long there, faithfully serving it, bonding with its people, etc. Every action a person takes indirectly affects their country (i.e. public interest: the interest of those sharing one's country—its resources, laws, problems, etc.), before affecting the entire world.
The favors between citizens and states can be shared for present, past or future reasons: you help your country because it helps you now, had helped you before, or will help you later (you plan to live, grow old and die there).
"A bird in hand is worth two in the bush": living in an unknown environment may have more risk than living in one you know. Other than the physical, there are social and psychological benefits making life generally safer and easier with fellow citizens: shared language, culture, traditions, memories, identity, and roots that can't exist elsewhere.
However, sometimes when citizens suffer much at home or feel unwelcome there, and all possibilities to cope with life there are exhausted, they should consider alternatives. This is usually the fault of other citizens, not the country (that has survived for ages for its unique, natural and developed character: people come and go, but nations remain). So when some disloyal citizens breach the pact between them and their country, they make life difficult for other innocent citizens who are indirectly forced to leave.
Thus, it's always good to learn about other countries (whether for migration, cooperation, knowledge ... or diversion), comparing the physical and emotional cost of applying, traveling ... and living there, to life at home, before making a decision.
We "enjoy the past" in our homeland more than any other place, as we can find there more evocative objects, places and people to communicate with, connecting us with our origins. Our memories help us understand ourselves better, giving unity to life's different stages from birth to death. Sometimes, citizens help their country merely for those pleasant memories that shaped their lifelong personality. Even though they are saved as mere brain signals, they affect other brain parts all life long. Connecting with one's past is useful for better self-understanding, reclaiming lost advantages, honing old skills, evoking old pleasures, etc.