There are already laws protecting freedom of expression, so I think it's disingenuous to suggest that CU is all about freedom of expression, and therefore good for democracy.
It doesn't really open the door to no-limit campaign financing. It says that the government can't put a limit on how much money a person or group of people (like the "Citizens United" nonprofit--hence the name) can spend to promote their OWN opinions.
There is a difference between 1) giving a political candidate $1 million, and 2) spending $1 million to shoot, print, and promote a documentary movie about a political candidate.
#1 is still illegal. And it's hard to imagine a way to limit #2 without giving someone the power to determine which movie (or website, or podcast) is "legal" and which is "illegal" speech about a candidate.
If we can't speak freely each other about candidates, how can we hope to have a valid political process at all?