FOX asserted that there are no written rules against distorting news in the media. They argued that, under the First Amendment, broadcasters have the right to lie or deliberately distort news reports on public airwaves. Fox attorneys did not dispute Akre’s claim that they pressured her to broadcast a false story, they simply maintained that it was their right to do so.
In part, this is a case of a good legal strategy which is a bad PR strategy (they won on this argument in Court). But, every other news organization worth its salt has an express written policy that it will not lie to the general public about anything, of strictly separating the business side of the business from the news side of the business, and of providing reports and editors with some sort of recourse within the organization, at least, if this policy is violated.
Also, while FOX did win, the stronger part of its argument is that there isn't a law preventing what they are alleged to have done, not that the First Amendment prevents laws against news organizations deliberately disorting the news. It is well established that intentionally false (or even recklessly false) statements may be prohibited and punished consistent with the First Amendment. Such statements are routinely held to be illegal with valid laws in defamation suits, deceptive trade practices suits, perjury prosecutions, fraud suits, suits alleging false medical claims, securities fraud suits, and deceptive trademark infringement suits, for example. First Amendment challenges to laws prohibiting false statements almost always fail.