But when a subreddit is part of the default selection of subreddits (for non-logged in users), that has a fairly large impact for the userbase of Reddit in general. And if it is part of the default, then the normal user (someone that doesn't mess with their subreddit selection much) would also be impacted.
Isn't that even more of a reason to remove the article?
It was posted to more than 1 default subreddit, including /r/worldnews which is larger than /r/news. That means you're going to have multiple submissions of the same article on the front page. Duplicate content on the front page doesn't give a good first impression, it looks messy or even spammy. It also takes up valuable space for people who may not care about the topic.
