Why? (spoilers)

The idea seems to be that the dog, having been reprogrammed to no longer attack black people on sight, now attacks white people on sight. Even though that was not the intent of the trainer working with him.

I know. It makes no sense.

Alternatively, perhaps we're supposed to think the dog is confusing the Burl Ives character with the man who trained him to attack black people, since that actor very slightly resembles Burl Ives.

Which makes no sense either, of course.

The book this movie is based on ends with the dog attacking two white men because he's been intentionally retrained to do so.

That's what the movie is referring to, but with the story having been so radically rewritten, this scene no longer has any basis. Fuller tried to work around this by having the trainer say that a dog being retrained could go insane, but there's no basis for this in any training literature I've seen. Either the retraining would work or it wouldn't. The dog is just doing what he was told, either way.

the dog has been dramatised by childhood experiences, (man, in hollywood they have vet psychiatrists as well heheheh)

Here a black man is kind to him, so the dog then thinks that the whiteman must be the danger...the dog is all confused!

the director adds a psyschology depth that confuses clyons.

that makes the film stronger as anti-racism than a vengeance film of the dog retrained by black racists to attack whites, which is what clyons loves

I took the ending like this: Throughout the film, the dog was aggressive when ever a man came around Kristy McNicol's character, ever since she was attacked early in the film.

I simply took it to mean that the dog didn't recognize Burl Ives and took him as a threat, and that's why he attacked. Knowing the dog was a killer, they decided to put him down.

The movie isn't just an indictment of racism, but of hatred in general. Hatred serves nobody, it just causes more destruction.

I didn't get that or the fact the dog attacked a white guy who attacked the main actress.

To me, attacking two white people and three black people doesn't make the dog a White Dog, as defined in the movie. I am talking about the people who the dog attacks, not the trainer, who happens to be black.

Maybe I should read the book because that seems more interesting. That a black trainer would retrain the dog to attack white people. This film has a very interesting idea, it just isn't followed through very well. Any assumption that the dog is white dog is just theory from the characters...but maybe the book makes it clear.

I don't think the ending really made any sense at all, but I'm going with the explanation that Ives looked like the previous owner, so the racial theme remains intact. Although a better explanation would be that the dog just attacked people for no known reason and they were wrong about him being a white dog.

The dog had been trained to attack blacks and so the dog only attacked blacks and not white people. I haven't seen the movie in a while so I don't know whether the person who tried to harm Kristy was white. Anyway, the black man(Keys)retrained the dog to not attack blacks. Keys thought that this would solve the dog's problems. What he expected was that the dog would understand that blacks were not to be attacked and, since he had never attacked whites nor been taught to, he would not attack them either. But the dog mistook the training by Keys to mean that whites were to be attacked and not blacks.