We do have a bit of an unofficial source blacklist. Write up a list of outlets that you think shouldn't ever be used as a source and submit that to modmail. We can have that discussion, but it's not going to be as cut and dry as you think. There are going to be people who disagree that Politico should be banned. Some people will think Fox should be banned, and others will think CNN should be banned.
We do have a more hands-off approach than most subs, but we do remove posts that are misleading, especially if we can clearly and easily tell that the post is misleading. If it's debatable, or if we are dealing with our lives, it will probably stay up for some amount of time at least and the comments will take care of any issues. The post can easily turn into a criticism of the article itself, which happens all the time here. The way I approach this is to try to not babysit the subreddit too much, and remove the shittier content when I see it, trying to stay objective and fair. If I arbitrarily start adding all of these outlets to the blacklist because I have a negative opinion of them, I'm going to get a lot more shit from the users than I get right now.
I don't remember the last time Brietbart was used as a source. I recall it being posted probably 3 times per year, generally with negative or very little upvotes. I'm sure you'll be able to find an example somewhere, but Brietbart is not a problem for this sub as your comment insinuates. A quick glance shows the only recent link to Brietbart is a criticism of it.
There is also the issue of which outlets have the motivation to criticize other media. Media criticism comes from the media itself all the time. Blacklisting an entire outlet means even the few good journalists who work for that outlet and put out good content can't be posted. I don't see this as a black and white issue. An outlet that you don't like can post true information, at least some of the time.