|June 28th, 2012
One thing they tend not to distinguish, however, is whether the catastrophe threatens to kill everyone or just most people. In terms of how many people die, things that kill 90% of people vs 100% are much more similar than different. But anything humanity can't recover from is very much worse: it removes the possibility of future people getting to live.  I find plagues and bioterrorism really worrying, but at least they're very unlikely to kill everyone.
 Except love. The author can make a romance much stronger by having the protagonist make a choice where they value the love interest more than saving the world. Of course the world still gets saved, potentially by the two of them working together.
 If there might be a lot of future people this is really bad, but even if we're just talking about a eliminating the earth's steady state population that's a lot of people-time missed out on.