Hmm. This is a hard one. This is all a matter of opinion on what an equal punishment for any given crime is. When I say equal, I mean such a punishment that the amount of good done is the same as the amount of bad/evil done. This is probably one of the hardest things to measure.
The whole 'an eye for an eye' thing would be the greatest, most fair way of deciding a punishment, only if by taking the person's who did the wrong eye, you could give it back (fully functional) to the person who had the damage inflicted on them to begin with.
So, in your case, I believe that it would be ethically correct to hack the racist website, as it would return the "right to be who you are" back to the targeted race.
Now, make sure that you are understanding the web site's FULL meaning. Maybe it looks like they are targeting a specific race, when really, they are targeting a specific group of people that happens to be in that race. For example, maybe the site is only targeting 'gangsters', who are predominately black. Or perhaps they are targeting the KKK, predominately white. Then, I believe that the punishment they are administering is fair.
I usually don't read every post in a thread before I reply to it (maybe not the greatest idea.)... anyway, I did catch a glimpse of 'freedom of speech'. I thought to myself "if by acting upon your freedom of speech, it oppresses someone else's freedom, especially someone Innocent's freedom, should freedom of speech be a valid defense?" And my answer was no, it is simply ludicrous to destroy a person's, or group's of people freedom, and then say that you have the freedom to do that. Hypocrite.