Wonderful sentiment, but unrealistic.
Unfortunately the world is and will be for some time divided into nation states. Ours for the moment being the UK. Now unless you would be happy for these islands to be ruled by someone from anywhere in the world, (say Germany or Argentina for example,) you are in small part, a nationalist. ????
Perhaps a "British" nationalist.
I also hate certain types of nationalism.
I have no problem with nationalism that is inclusive of all in a nation despite their background, is based on the principle of self determination and is not expansive or seeking to dominate others. Very much the Scottish example.
I hate nationalism that is overbearing, expansive and seeks to deny other persons the right to determine their own destiny.
It is not the fact that peoples and nations are different that causes problems. There is always going to be differences.
The issue comes when nations cannot accept that other people are different. They seek to dominate . That is the true evil side of nationalism.