Merriam Webster definition of a nationalist:
: an advocate of or believer in nationalism
: loyalty and devotion to a nation
especially : a sense of national consciousness (see CONSCIOUSNESS sense 1c) exalting one nation above all others and placing primary emphasis on promotion of its culture and interests as opposed to those of other nations or supranational groups
2 : a member of a political party or group advocating national independence or strong national government
No one should have to apologize for being a nationalist.
I think you're conflating Nationalism with Patriotism. Nationalism is like Jingoism, without the military aspect.
Nationalism is about cultural superiority. That is what "exalting one nation above all others and placing primary emphasis on promotion of its culture and interests as opposed to those of other nations" means. In today's parlance, it's come to describe people or groups that think their culture is superior based on race or creed. Like a white nationalist or black nationalist. Groups like The League of the South, the KKK, Black Panthers, Viet Cong, Workers Party of Korea, Ba'ath Party, the IRA, the Nazi party...in fact if you take a look you'll find that many Nationalist groups are often time socialist or communists.
Having pride in your country is Patriotism.
For example, I'm proud to be an American. I love this country, I think for all its warts and problems we're a great country. But I don't think we're the best thing since sliced bread and every country NOT named the USA can take a backseat. I don't think the rest of the world should tremble before us.
Thinking your country is morally and culturally superior is completely different than having pride.