The argument you offer is entirely speculative; there’s no evidence to support it. There is some evidence available to us here: the placement rates of graduates of journalism schools. I did a little poking around on the web and found two sites with placement rates:
Now, if placement rates were low, then we would at least have some information about how often J-school grads get turned down, but the data here is just not sufficient to support any conclusions.
I’ll counter Mr. Chomsky’s speculation with one of my own. Let’s speculate on the kind of person who would be motivated to enter journalism school. I would speculate that the people attracted to that kind of career are motivated by a desire to right the injustices of the world, to fight truth to power. This speculation suggests that journalism school students are probably more leftist in their attitudes than the average American. I think my speculation is better than your speculation (nyaahh, nyaahh, nyaahh), but at this point our difference is a battle of hot air.
I’ll also point out that conservatives have long complained of “the liberal media”, so they’re pushing a conspiracy theory, only it’s the opposite of what you’re pushing. A Martian trying to make sense of this would probably poll lots of people and come to the conclusion that more conservatives than progressives complain about bias in the media, ergo the media is probably more biased towards the left. I reject this line of argument because I believe the dictum that “Reality has a well-known liberal bias.”