Well it already is a racial slur, but I'm guessing that that you mean by your post, OP, is "should it be as controversial a slur as "******" or "slope" or "wog"".
Call me extremely stereotypically white, but yeah, it should. Like many of the whites on here I'm not particularly offended by it, but I am offended by the fact that ethnic minorities are allowed to be racist against both whites and other ethnic minorities. I'm offended that that is not considered racism. There was apparently some philosopher on such matters in the 70s or something that said that racism = prejudice + power, and in that sense white people are the only people who are able to be racist (at least in English-speaking countries). I call bullshit on that one, and I am pretty sure that anybody of an ethnic minority that is not a total prick probably refrains from using the word "cracker" when not talking about Jatz or Saos.
Racism is a difficult issue, because there is a lot of it still around, even if people don't necessarily consciously realise it. Ideally we want to get to a stage where everybody is treated equally, and allowing ethnic minorities to use racial slurs is causing more problems than it solves, because it's giving ethnic minorities something that whites aren't allowed, as it were. I object to whites being given something that ethnic minorities aren't allowed as well, to be perfectly clear. My point is that having two sets of rules for different sets of people is doing nothing to help us reach that ultimate state where everybody is equal.