Because the Torah repeatedly calls us to care for the poor, the widow, the orphan, and the alien. Because the prophets and the psalms and the wisdom literature all hold this out as a criterion of our faith. Because Jesus leads us in reaching out to outcasts and caring for the least in society. Because the epistles and the Apocalypse speak of it as well. In other words, the entire Bible calls us to pursue social justice.
And, because y'all know I won't resist, Glenn Beck is an ass. And a false prophet.
1 John 4.1