Yeah, if they actually wanted to censor something they would do it silently, by not showing it in people's news feeds. Proving such practice exists would probably be near impossible without having access to the source code or core usage statistics.
This just makes me wonder exactly how automated that feature is, because surely a non-nominal number of people share current event links all the time about something political, sporting event, natural disaster. I wonder if it happens then, or is this a matter of recency....Streisand (there's got to be a better word for it than that) following the news of those 50million accounts being breached.
1. Viral content like "share this or Facebook will delete your account" - may as well shut that down straight away.
2. A security flaw in a Facebook site that lets malicious websites post to your wall automatically from a webpage. In that case, the malicious website will probably post a link to itself, so that it can collect more victims. In this case, this limits the impact of the flaw. Look at the Samy worm as an example.
3. News feed algorithm "breaks" in some way when a lot of people are posting the same thing, so they just prevent that from happening.
Not really. Reddit does exactly this. Posts to /r/news are only allowed from a whitelist of "real news" sources.