Hate speech--in this country, principally racist and anti-Semitic speech--has always been recognized as First Amendment-protected. There is no First Amendment exception for hate speech, so unless it fits into one of the other pigeonholes--libel, obscenity, or fighting words--it receives the same guarantees as any other speech.
In recent years, the Supreme Court has held in RAV v. City of St. Paul that an ordinance aimed at cross-burning was an unconstitutional content-based regulation because it only banned cross-burning which constituted hate speech (an ordinance which banned burning any wooden object on lawns might have been constitutional). Also, a federal court recognized the right of the American Nazi Party to march through a Jewish suburb of Skokie, Illinois.
In a 1950's case, Beauharnais v. Illinois, the Supreme Court upheld the constitutionality of a state "group libel" law, which gave racial, ethnic and other groups the same right to sue for libel as individuals. Although Beauharnais has never been over-ruled, it is almost certainly a dead letter in light of RAV and numerous other cases.
Canada, Great Britain, Germany and numerous other Western democracies ban hate speech and there is an ongoing debate whether doing so undermines the fundamental tenet of a liberal democracy. Professor Catharine MacKinnon in her book Only Words draws the parallel between hate speech and pornography and observes that principles of free speech and equality are at war in this country. Nadine Strossen, president of the ACLU, replies that laws against speech are always used to ban unpopular minority speech rather than well-settled majority vices or prejudices. Just as Canada has used its official adoption of Mackinnon's principles to ban gay and lesbian speech, while mainstream pornography thrives, British hate speech prosecutions tend to target black groups rather than white skinheads.