Whether it's good or bad depends on whether your country acts ethically or not.
Instead of unconditionally supporting a nation, support good behaviour. If your nation acts well, all the better.

and since ethics are subjective..............

Not entirely. There are subjective moral sentiments, and then there are collective moral sentiments. There is no denying the existence of intersubjectivity in our passions (ie, we all want to avoid fear and suffering).
What really varies are ideas for the means to these goals (improving economy, making peace, pleasing Allah, killing all Jews, etc). But these methods can of course be discussed and scrutinized through reasonable discourse.

I can go to a remote Amazon tribe, and they will still be disgusted with the story about the holocaust and how millions of people were murdered.

Certain ethical outlooks are a prerequisite for the lasting community of beings like us.

And yet I doubt you feel the same disgust for the murder of German soldiers, no?

Naturally, because they were assaulting 2 (more or less) universally agreed passions, causing suffering and fear all around. That is not to say German soldiers even thought they were being ethical, though. We don't always do what we think is right. Many of them were likewise victims of pressure and brainwashing.

Odlov i can't understand well if you are assuming the existence of a common moral..

I'm not assuming any transcendent "moral absolutism", I'm just looking at the few common values people hold and working from there.

-Eating lots of sugar is unhealthy.
-Not for me! I have hypoglycemia! LOL what's healthy is completely subjective!

-Hey, that person is fat.
-Fatness is subjective! He may be fat to Ethiopians, but not to Americans! Statements about weight are meaningless hurr durr

So I just read about what nationalism actually is. There are two things why I think that nationalism isn't good. First one: Every bigger group with the same origin, history or ethnics has a right to statehood. So how big does a group have to be? I think that that is subjective, which leads to wars due to different oppinions.

The way bigger problem is: Individuals define themselves with their nation and only with their nation. That is just wrong. Just because I speak the same language as someone or have the same history I am not like him/her.

I think people should act and group because of their views and oppinions not because of their language or history.

e: And of course the view that the loyalty towards my nation is the most important one is just wrong, too.

So you feel no disgust at the murder of those who were too victims. I am sure you could find people who think this is unethical.

So once again, even your 'universal' ethics can be warped by perspective.

Pointing to differences in opinions on what is ethical doesn't mean there are no collective agreements in our passions - clearly there are (as I have pointed out earlier).

Likewise differences in opinions on what constitutes 'healthy food' don't mean matters of human nutrition are completely subjective. Clearly some diets are universally more harmful.

I never argued for moral absolutism - only intersubjectivity. Overwhelming majority of people in the world will agree when you say stabbing a stranger is wrong - that's all that matters.