Reddit has large radical left and radical right communities that are constantly fighting and overwhelm the site with political drama and propaganda. If they don't do something about it they are going to lose the users that come there to look at cats.
That's the problem -- there should be no "Reddit". The only interesting part of Reddit are the communities and there's no reason why the_donald and SRS can't exist under the same reddit.com domain. I really wish /u/spez et al. would take a hands-off approach except for cases where users are breaking the law.
I disagree. As nice as it would be, subreddits do not exist in isolation from one another and very often, trends and behavior set in one subreddit trickle to others. This was noticeable leading up to the removal of /r/fatpeoplehate et al, and it's noticable right now. The flamewar between the radical left and right flows onto almost all default subreddits, and it does drive overall quality down.