The wikipedia summary (https://en.wikipedia.org/wiki/Citizens_United_v._FEC) is pretty good. The government can't prohibit anyone (people, corporations, unions, etc) from making political speech, so long as it's not directed by the candidate. So I can't donate a billion dollars to a candidate's campaign, but I can run a billion dollars of ads supporting him (or against his opponent), so long as I don't receive direction/instruction from the candidate. Or, in this case, make and advertise a movie. The question you have to ask yourself is whether the alternative would be worse.
That wasn’t the “outcome” of Citizens United. The outcome was that the government can’t punish a small non-profit from making a movie critical of a candidate within 90 days of an election.
You can read whatever you want into the implications of the rule articulated in the case. Folks on the other side can say that, if the decision had gone the other way, nothing would stop the government from regulating how the New York Times uses its corporate funds.
But it’s important to look at the actual case, legally because it is really the only thing that’s decided, but practically because it is an actual conduct the government decided to prosecute. The government didn’t think the law just covers billion dollar advocacy campaigns. It prosecuted a small non-profit entity for publishing a movie. It’s not a “parade of horribles” hypothetical consequence, it actually happened. The “alternative” would be allowing the government to prosecute this non-profit for publishing a political movie.
Maybe outcome is not the right word then...but I was trying to capture the concept of downstream consequences. In the same way that you could say that an "outcome" (or whatever word is better) of Title VII of the Civil Rights Act is that employers cannot fire workers for being gay or transgender, even though those intentions weren't even on the radar when the law was written. On the third hand, it seems wrong to call Citizens United an "outcome" when it's more like a clarification of an existing right, as opposed to the granting of a new one.
I also don't disagree with the court's ruling, I was just trying to phrase my response in as neutral a way as possible.