I do not include people like you in "The side that opposes"

That is a logical and fair view of nationalism.

But the... i will call them leftists... don't have any such arguments. Currently they are saying white american's bad. They throw anything they can, such as white american's had slaves... although white american's were among the first to free slaves. But that isn't brought up. It is just, "those people are bad"

An example, they call everyone that doesn't agree with them "Nazis" (not-Cs). They do this because Nazi is a bad word to most people, and so, they are using the worst word they know to make them feel as bad as possible. However, they do not know what the word means, or what it implies. Bernie Sanders said he was a national socialist. Nazi stands for National socialist.

Now, about nationalism.
A person needs to have a fair amount of self esteem. Too little and they cannot function. Too much and they are a pain to be around, usually getting people hurt by not knowing their limits.

Having pride in your group is important. It is the glue that holds the people together. Too little and the group falls apart. Too much and they get ideas of being better than.

However, it is really T.H.E.M. who take the patriotism and turn it into war. By creating false flags, and then saying to the patriots, "they are attacking us", T.H.E.Y. have gotten us into many wars.