If one believes that our social problems are caused entirely (or nearly) by a lack of generosity, or empathy, or tolerance, or justice - or at least if one believes that the solutions to those problems depend entirely on generosity, etc, then the line to self-righteousness is direct. Notice that this is true even if that assessment is entirely correct. Even if lack of tolerance and empathy are indeed the main problem, when one attempts to engage others in solutions, self-righteousness will get smuggled in. There just isn't any other ground to stand on when one says "our side believes that more generosity is the solution." Squirm as you might, that can only mean "Our side is more generous," which can only mean "we are better people."
It might be quiet rather than brash. No matter. Others can sense it even if you cannot.
It may include some laudable desire to keep that arrogance confined to the ideas one holds rather than one's own character. I have known those whose humility exceeds mine in a dozen areas of their personal lives, who approach the quest for justice as a personal challenge, who resolve first to clean up their own act before whispering a word to others. Some are lovely, sincere people. Not many, because such humility is confined to specific sectors of their lives. I have a significant advantage here - or perhaps it is a curse. Because I engage folks in a wider range of topics, and sometimes even seek the difficult ones (if I think you are smart enough and strong enough), I elicit amazingly revealing comments from people all the time. They might say the same of me, by the way. I am familiar with the enormous arrogance of humble people. Their personal Screwtape has channeled all the poison into a single pond on their property. Projection is simply thinking that the speck in your eye is a log in another's. Jesus used the image of tithing mint, dill, and cumin. He didn't say the Pharisees weren't very, very, good at that. They were far better than we are at those specks.
Christians have a particular danger in this, in that they try to cop to a lesser charge. Preachers do it a lot. I would not be too hard on them for that, because it's mostly just because they get the opportunity to, having to give personal examples every week. We would be worse. "Yes, I too know the dangers of materialism (or privilege, or selfishness). I fight this battle all the time, just as you do. Let me tell you a few anecdotes of when I was not generous..." These are declarations of righteousness, not humility. I don't have this problem to the extent that our whole society, including you out there listening, does. I have small sins, you have medium sins, those people outside this sanctuary have big sins.
There are other escape routes. Some will say "Well, we are more moral. It might sound arrogant to you that we say that, but it's true. We might have our individual flaws, and I might be a complete hypocrite myself, but the ideas are more moral. You, AVI, are simple evading that." Some Christians might even add "Of course those ideas are more moral. They are what Jesus said. Deal with it." I think those are answerable. In fact I think they are easily answerable, though not quickly answerable. That they persist in the face of the many times they have been answered is revealing of human nature.
Others might wave off the moral questions entirely. "These are all merely questions of power. Those who have power invent moralities to keep themselves in power. You have power, we want to take it from you. And because you have kept it from us unjustly for so long, we are entirely comfortable punishing you for it. How does it feel, eh?" This sentiment is not merely lurking at the edge of our political discourse, sniping in from the shadows, it has moved to the debate stage, though in disguise. I give it credit that it is logically coherent. I think it is also answerable, but also not quickly, and not today.
This is aimed in a different direction, at those who would wish to be humble and tolerant themselves, especially those who are believing Christians or believing Jews. There is an elephant in the room.