It's all about self-interest. Greed (or if you prefer putting a nice, socially acceptable gloss on it, call it "career aspirations").

Why are so many seemingly respectable journalists who came up through the ranks at real journalistic institutions such as NPR perfectly willing to jump to Fox?  The answer is the same as why they tolerate the moonie paper:

It's a job.

There aren't THAT many jobs in "journalism" (I'm using the term loosely here). Fox or Moon pay as well or better than "real" journalism jobs.  But most of all, they pay.  And they provide visibility.  See mom and dad? I'm a famous journalist!

For someone who decided that they "want to be a reporter when they grow up", the odds of actually landing a paying gig at something larger than the County Gazette are pretty slim.  There's a lot of would-be "reporters" who major in "communications" or some more specific program in college whose aim is to nail down a job as a news anchor. The chances of that happening are about the same as the chances of your average kid with a guitar has of becoming a top-of-the-charts rock star, or the chance that somebody who "likes to paint" has of becoming the next Picasso. They go to school, they tell their family their dream is to be a famous journalist. But it becomes pretty clear pretty quickly that there are many thousands of people with that same dream and only a small handful of paying jobs that even come close to the picture that they had of what they would be doing someday.  

Some of these people will quit the business. The more physically attractive ones go into TV (the number one qualification for any work on-camera). Those with beautiful voices go into radio. Those who were not born with such gifts might try writing (although these days, that's not considered very attractive - not as much glory). But few get a chance to work in any job that even comes close to what they had hoped for. This isn't so different from a lot of career paths -- you have a chance at what appears to eb a great gig, and you don't worry too much about the details, you go for it. That's capitalism!

So you have manufactured institutions come along like Moon or Fox.  Few apiring "journalists" who are desparate for "their big break" can resist the lure: high profile jobs, big pay, "fast track".  Those "journalists" who might not be quite so desparate (i.e. already fairly well employed) also know that the business is fickle, and that there are few jobs. Why try to destroy an outlet that might one day be your paycheck (newspapers close, stations reorganize, people get replaced by someone with better hair, etc.)?

Why do people tolerate nut-job propaganda organs like Fox and the Moonie Times? For the same reason that most everyone (with few exceptions) are willing to appear on Fox....self-interest.  From Lieberman to Hillary to others, nearly everyone is willing to hold their nose and deal with the devil because of the lure of publicity/money/career/some other personal advantage is too great for most to resist. Who can resist the bright lights?

It's a tough nut to crack. We live in a society where one learns very early that you need to do everything and anything to advance your own interests. When put in the difficult position where your own personal ambitions might benefit from dealing with a compromised benefactor, it shouldn't be a surprise that the comprosmiser often wins out.

People figure they have families to feed, kids to send to college, golf to play in St. Vincent, etc., etc.  Moon's money or Murdoch's money will pay those bills better than Frontline's or Mother Jones'.