Dogs do not understand the concept of racism!

I used to have a dog who would growl and become more aggressive at people of darker skin, actually. That's part of the reason why I watched this (aside from the fact that I enjoy Sam Fuller movies), because I thought it was interesting that somebody made a movie about something like that. I used to have a neighbor, about 10 years ago, who lived in Africa with the dog that she would eventually give my family (she ended up having another child and couldn't take care of the dog anymore, it became too much of a burden). Before we took her, the owner told us that when she was a puppy in Africa, local boys who happened to be black would throw rocks at her when she was on her leash in the backyard, and she told us that she can become rather aggressive towards people of darker skin. Now, she didn't become quite as vicious as the dog in this film does, and ironically my dog was a black one, but I wouldn't say it's not possible for a dog to hold some kind of negative response towards a group of people or whatever after being traumatized at a young age.

Agreed. Humans do not understand "racism" either and that is why this film and anti-racism in general is a farce. When people refer to "racism" they're typically referring to something that should more appropriately be labeled as "skinism" or some such descriptor. Racism has very little to do with actual race and is more related to judgmental stereotypes based on the color of skin or other visual/aural stimuli. People perceive the world through their own particular "reality tunnels" and belief systems on a daily basis. People will always judge others and commit violence against others for a number of reasons -- and they should -- we're animals after all. That's about the only thing Fuller (unintentionally) got right with this film.

this movie wants you to believe that a dog has a human mind which exclusively hates blacks

A bird sings and the mountain's silence deepens.

A movie can use imagery which symbolizes something without me needing to "believe" anything. I think you are reading into it too literally.