Is nationalism a perversion of patriotism?

To me, patriotism is taking pride in the country you are from. Whether or not it makes sense to have any pride in being from a certain country is a question to which I have an unpopular answer. That aside, nationalism, to me, is when you essentially disregard people who are not from your country when making decisions. That means you are not interested in the needs of anyone outside your country, including prospective immigrants, refugees, and even sometimes foreign-born citizens of your own country, and you're doing all this in the name of "taking care of your people first" when really it's all about saying "fuck you" to all foreigners.

a sane response I think but I do not really understand what you mean

Yes. It takes the love and gratitude one has for your nation and turns it outwards against others. as hate and envy.
And in the current situation, you know you are in the Merde when the French have the moral high ground.

What's wrong with thinking that your own people are more important?

It's the opposite of patriotism

No

Yes.