[onewhippedpuppy]

Fiduciary duty pretty much sums it up. However, in recent years it's been shown that social responsibility can be used to boost profits. The stupidity of a $7 cup of coffee at Starbucks can be rationalized with the knowledge that Starbucks works to insure the working conditions of their Central American coffee farmers are up to par, and that they are paid well. So while I don't think it's a specific duty of businesses to contribute to charities/etc, the good PR can often spin into increased profits.