I am not the one who responded with “there would be one less white idiot”; therefore, I cannot take responsibility for what other people say. However, “white idiot” is not a racial slur. White is the race the person is. Idiotic is a trait they were exhibiting.
White people do not experience racism; however, white people can experience prejudice and/or discrimination.
The person you originally referred to is posting racist images against Native Americans and used the excuse that because he “fought Nazis” that it somehow exempt him from being called a racist; when, in fact, he was and is being racist. So when a person of color insults this man, who is harming them with his racist photos, it is not racism when the victim insults their oppressor.