Why are atheists worried about the false rapture date (May 21)?

If you don't believe in the Bible, what are you worrying about? If you do believe in the Bible, then you shouldn't worry, considering the rapture date that Harold Camping concocted is not Biblically accurate. True the Lord will come soon, but like a thief in the night and we will not know the day nor the hour. Keep in mind there are some additional things which must happen before the rapture is to take place.