Why do stocks keep going up?

The Dow gained another 72 points in today's holiday-shortened session and is within 57 points of getting back over 13,000. Don't try figuring this one out - despite some decent economic news today (car sales were up nicely in June and factory orders rose in May for the first time in three months), the outlook over the next six months is not wonderful. Two possible explanations: A weakened economy could prompt the Federal Reserve to inject more stimulus into the system, and U.S. equities have become the lesser of investment evils.