I had a bit of a discussion (read: argument) with a friend of mine last night over this very issue. I don't think either of us convinced each other, which reminded me of why I despise having debates on Facebook because it largely is for naught in terms of persuasion. He made an interesting point which I had not considered, which I really disagreed with but was a serious fundamental difference that was not going to be resolved through Facebook snark. (I admit now upon sleeping on it that I should have just walked away and not gotten involved, which I usually try to do, but, hey, we all make mistakes...)
His point was, coming from a Southern Baptist Evangelical position that "that you have to get the doctrine right, or else there can be no ground for social justice." His reasoning was that everything flows from Jesus, which had a logic to it in its own way, though I vehemently disagreed. Yes, Jesus is central, but like David said above, you don't feed steak to a baby. That was where, I think we fundamentally just had to agree to disagree because Protestants of this ilk, God bless them, are so focused on getting every dot and tittle of doctrine correct that greater unity in any meaningful sense is largely off the radar.
I call this Sola Doctrina, by Doctrine Alone, which I think is very dangerous because it is fragmentary by nature. Everything has to do with pre-assumed doctrine as primary and central and, ironically, not the Word of God or Holy Tradition or even the person of Jesus Christ. In other words, our doctrine is what we base everything on, which, hilariously, is the heresy they accuse Catholics of, that Catholics don't base what they believe on the Bible, which they don't really either.
But, back to the topic at hand, as Catholics, we have a great theology of Natural Law, that God has included in the heart of every man a reason and a reflection of the Divine moral law. People may not have the full revelation of Jesus Christ, but all people still have an echo or fingerprint of the divine moral law on their hearts. That even if they have never heard about God or Jesus or what have you, their God given reason through Natural Law can at least for brief periods, allow them to stand up on tippy toes and peer in and get a glimpse of the Kingdom of God. This is why many of the Early Church fathers incorporated part of Greco-roman philosophy into their theology because they believed that even in the absence of Christ, philosophers like Plato or Aristotle could get glimpses of the Kingdom of God, though they did not have the full revelation of Christ. That seed of Natural Law was still bearing fruit in their writings, that God could still speak to them and through them in some small way apart from the Incarnation. Original Sin had marred and separated them from the Divine, but that fingerprint of the creator was still found within them.
To Evangelicals who think you have to get doctrine right first or you can have no real social justice rejects this notion of Natural Law. They believe that all men are depraved and cannot in any way see the good or work for the good, that, in essence, man is so corrupted that even the fingerprint of the divine has been so marred that humanity is totally incapable of anything good, regardless of reason or innate moral law written on all men's hearts.
Sadly, I think this is a fundamental difference with our Evangelical brothers and sisters that is very much at the heart of this snarking at the Holy Father's address to Congress. He did not mention Jesus specifically, through he did mention God 9 times and was speaking to things that Jesus specifically preached about helping the poor and orphaned and being kind to the aliens among us. As such, they think the speech was a failure. And, maybe is was, maybe it was not. The point is, the Holy Father was planting seeds. Whether they bear fruit or not is not for us to argue. It's the Holy Spirit that grows the seed. We're called to be witnesses to Moral Truth and to sew the seeds and leave the rest in God's hands.
Seeds come in all forms, not just in naming the name of Jesus like a magical incantation.