Black hat is a derisive term for seo hackers who game the system by whatever means is necessary. The concept is not unethical by nature, but some activity labeled black hat is.
But before you get too judgmental, remember that link buying and selling are now (just recently) considered black hat activities - Google is even asking that you report any site known to be a seller or a buyer of links. See paid links.
So an entire segment of our known seo universe that has been flourishing openly for years, is now suddenly and officially 'black hat.' Think about that and you start to migrate away from the misconception of black hat as evil.
In fact, black hat may be the key to survival. Don't want to mislead you into the wrong religion here, but you may want to keep an open mind if you thought you'd never go there. Remember, being outside Google's guidelines is not illegal, and not even unethical - don't let one corporation's arbitrarily defined rules determine your ethics.
Let's look at some realistic ethical issues in the world of search.
Your closest competitor just took your #1 ranks using black hat techniques, and when you report them to Google (as they have asked us to), nothing happens.
Your site is penalized in google by the actions of others, but Google expects YOU to unwind the issues before releasing your site.