Nationalism is healthy when it centers on positives about the country. Being proud of good things made or achieved by people from your country is fine, for example, especially as a call to action for achieving further good.

It is unhealthy when it centers on negatives about other countries. Being proud that you're so much better than those lazy freeloaders across the border is not so great, for example.

I tend to disagree. With nationalism/patriotism, you cannot avoid highlighting positivies of the past and skipping darker parts, which then gives twisted "we're the best country in the world" impression. US is a fine example, but I believe all countries are in, one way or the other.

One should view critically the past and present of its own nation, focus on all aspects, and learn from mistakes. But nationalism/patriotism and objective critical thinking tend to go against each other in real world out there. So no, I prefer to not like patriotism, of any kind. Anyway, I feel more of a citizen of this world, rather than some area that belonged somewhere else 100 years ago, elsewhere 1000 yeats ago, and will for sure in another 1000 years in future. Once a person moves a bit around the world, perspective on this topic is changed for good (classic House quote - "Patriotism is nothing but loyalty to real estate")