I do not like political correctness much either, and I'm no expert on ethnic and racial slurs, but we do have to make sure we treat this subject with tact. This reminds me when Bart Simpson attended church and on the way home announced to his parents that the words hell, damn, and ass are in the Bible so he was going to start using them. "Damn, let's get our ass to the hell restuarant".
I am actually a fan of the post WWII Japanese people. I appreciate the gains they've made and how they have been a supportive US ally. So no one could realistically call me anti-Japanese. I don't know if "Jap" is a slur that Japanese find offensive or not. I use it as short for Japanese, but if I found using it was causing friction, I would not use it.