How biblical is (much of) evangelical theology?

I was doing some reading on Friday morning and came across this article by Ronald Sider. Here's an excerpt that I thought was rather challenging for those of us who are middle-class evangelicals...

‘Lest we forget the warning, God repeats it in I John. "But if any one has the world’s goods and sees his brother in need, yet closes his heart against him, how does God’s love abide in him? Little children, let us not love in word or speech but in deed and truth" (3:17-18. [RSV]; cf. also James 2:14-17). Again, the words are plain. What do they mean for Western Christians who demand increasing affluence each year while people in the Third World suffer malnutrition, deformed bodies and brains, even starvation? The text clearly says that if we fail to aid the needy, we do not have God’s love -- no matter what we may say. The text demands deeds, not pious phrases and saintly speeches...’

‘All the texts from both testaments which we have just surveyed surely mean more than that the people of God are disobedient (but still justified all the same) when they neglect the poor…’

‘In light of this clear biblical teaching, how biblical is evangelical theology? Certainly there have been some great moments of faithfulness. Wesley, Wilberforce and Charles Finney’s evangelical abolitionists stood solidly in the biblical tradition in their search for justice for the poor and oppressed of their time. But 20th century evangelicals have not, by and large, followed their example. The evangelical community is largely on the side of the rich oppressors rather than that of the oppressed poor. Imagine what would happen if all the evangelical institutions -- youth organizations, publications, colleges and seminaries, congregations and denominational headquarters -- would dare to undertake a comprehensive two-year examination of their total program and activity to answer this question: Is there the same balance and emphasis on justice for the poor and oppressed in our programs as there is in Scripture? If those of us who are evangelicals did that with an unconditional readiness to change whatever did not correspond with the scriptural revelation of God’s special concern for the poor and oppressed, we would unleash a new movement of biblical social concern that would change the course of modern history.’