It seems C.S. Lewis thought it a demonic strategy to distract Christians from their primary mission by convincing them to treat Christianity as a means to advance social justice. Look what he wrote in Chapter 23 of The Screwtape Letters.
Keep in mind that the following is an excerpt from a senior demon writing to his nephew, helping him undermine the Christians he’s charged with deceiving. The “Enemy” is God.
We do want, and want very much, to make men treat Christianity as a means; preferably, of course, as a means to their own advancement, but, failing that, as a means to anything—even to social justice. The thing to do is to get a man at first to value social justice as a thing which the Enemy demands, and then work him on to the stage at which he values Christianity because it may produce social justice. For the Enemy will not be used as a convenience. Men or nations who think they can revive the Faith in order to make a good society might just as well think they can use the stairs of Heaven as a short cut to the nearest chemist’s shop. Fortunately it is quite easy to coax humans round this little corner.
My point is not that Christians shouldn’t care about the sick, the homeless, the widows, the orphans, and the oppressed. Of course we should. Our compassion and behavior should flow naturally from our faith and worldview.
We shouldn’t confuse that, though, with the central mission of Jesus, which was to preach the truth (Mark 1:38) and save that which was lost (Luke 19:10) by becoming a ransom for many (Matt. 20:28). Sure, he healed the sick and performed many miraculous signs, but these were also intended to authenticate his main message: the gospel.
Our role, consequently, is to be an ambassador for Jesus and to proclaim the message of reconciliation (2 Cor. 5:18–20). That’s our fundamental identity and mission. Though in the process, our love for all humanity should compel us to have compassion for those in need (and meet those needs!). But we don’t want to mold Christianity into our own making by using it “as a means to anything—even to social justice.”