As a German, I naturally have a special perspective on nationalism.
Is supporting your country, fighting and killing for it, valuable as an end in itself? If it was, the Nazis would have been the best people on this planet ever. Were the SS soldiers who actually believed they are defending their country heroes, when they murdered Jews, Russians and other "enemies"? Obviously not.
It's all about the values you believe in. When your country stands for just values, and fights a war for a just cause, then yes, people risking their lives to defend it are heroes. But defending it just for the sake of defending it, no matter what it stands for, does not make anybody a hero.
In the German debate, some distinguished between "primary values" and "secondary values": Primary values are values like honesty, kindness, humaneness, empathy, fairness and justice, love -- things like that.
Secondary values are things like obedience, boldness, punctuality, formal intelligence, things like that -- all values you can perfectly put to use to run an efficient death camp with. Without backup by primary values, these secondary values are worthless, dangerous even.
Patriotism as an end in itself is dangerous. When anybody places value in patriotism, regardless of the values your country stands for, he does not only overrate it, but makes a fatal mistake. Simply supporting your collective no matter what it does and stands for, or even supporting your government no matter what it does, is authoritarian thinking. It's the opposite of freedom and the opposite of democratic standards.
But there is nothing wrong with supporting a certain cause you consider just your country, government or collective engages in, and there is certainly nothing wrong with being proud of your achievements and the achievements your country you were part of made, in my book.