Louis CK had a quick segment on his "Hilarious" tour that said something about how "Jew" was the only such word that could be both the accepted term and a slur. The slur was just said with a little "stank" on it. He also talks about the little girl in "Schindler's List" standing on the mailbox and yelling, "Goodbye, Jews!"More now that I have a real keyboard.
For a long time, "Jew" was a slur because it was considering insulting to call someone a Jew. In some countries, the local equivalent is still frowned upon. In English, it's mostly no longer a slur. It's been reclaimed, or reappropriated, if you will. But, it can still be used as a slur, even in English. Such as when people use it as a verb ("I got jewed") or when, like a certain poster here, it's used in clever substitutions ("Jew York Times").
Language is complicated. Words that are insulting in some contexts and some times may not be in other contexts and times. One of the great powers of language is that it's not static.