If someone speaks out in praise of Osama Bin Laden, I do not think that the person should be detained for speaking his or her mind. I can see the need for protective custody if requested, but I choose to err on the side of freedom of speech rather than limitations on the same.
Holocaust deniers are allowed to spew whatever nonsense they wish in my country. This nation is none the worse for it, and they are rightfully seen by the vast majority of people as total fools. Fred Phelps is allowed to preach his hate-filled bile against gays. Because of this airing, people are far more aware of the dangers of hate speech, and he has been publicly condemned even by those who see homosexuality as a sin.
Freedom of speech is practical. Banned speech is dangerous, since it makes the government or religion seem scared of an idea or a concept. A government or religious institution that cannot stand up to open criticism and speech (however foolish or misguided) is not a government or religious institution worth defending.