Why do you think it's better to sacrifice privacy for security?
Well... okay, but without a warrant, doesn't that mean that the government has unlimited power as to how they spy on you? They can read your emails, or perhaps listen to your phone calls, as a warrant allows an authority to violate liberties, yet warrants also limit the liberties that can be violated. If the saying goes that "you have the right to remain silent" because what you say can be used as evidence in a court, surely that the FBI is able to do this is bad?
Yeah. And in some cases there are clear limits on what the FBI should be able to do ... but again, I don't really mind if the FBI scans my emails for keywords - they won't find any. As far as limiting their power does go, however, I'd much rather err on the side of security than on that of privacy. A 50/50 balance, while ideal, is impossible.