Okay, I think I know what went wrong: I'm not criticizing the content of anything SG said in particular, mostly because I actually agree with a lot of it, at least in principle. But there are several ways of approaching conflicts, and I'm saying that the one SG chose has a comparatively low success rate.
I admit I don't understand fully what you mean by the ideologies and perspectives of Social Democracy within this context. My best understanding is the essence is still competitive. There is still an upper class. But it's not so far out of reach of the lower class as it is here in the U.S. There are regulations that keep things from going too far. And those in the upper class don't make nearly so much fuss about giving back (although one of my favorite quotes from a politically radical businessman is "If you have to give back, you took too much"), in order to keep society livable for everyone.
Well yeah, that's what my ideal society looks like - but I was talking more about methods to reach a goal, be it a fully egalitarian society or the exact opposite, or something in between.
Let me try phrasing it as machiavellistically as possible:
If you're trying to reach a political goal, you have two options: Either gather enough force to sweep aside any resistance, or gather enough allies, support, mutual understanding to reach a workable compromise.
The first one seems better, right? You don't need to compromise, you get all you want and not just half or three quarters, you can free yourself of previous societal and political limitations, you don't have to listen to special interests groups... And all you need to do is get enough support in the first place. That may be hard, but it's worth it, right?
That would be true if the decision-making process happened only once. That's why this is a wise choice in an outright revolution, such as the 1917 one: You grab power once, and then you run with it.
In democratic systems however (and I don't think anyone here seriously wants to violently overturn them) the decision-making process happens again and again and again. Sure, you can ram through one thing, but you'll antagonise such a load of people and scare even those who supported you: You'll be able to ram through a second and third thing as well, but ultimately you're bound to fail.
This is why you need to adopt a less
confrontational stance: Always make it easy for your adversary to give in. Always make him think he's won, that you didn't fully get what you wanted. Don't insist on 100% all at once, but aim for 70% and then birng up the issue again at some later point. Always make sure that what you did doesn't hurt your adversary too much: Always make fighting you the worse choice for him. Embrace salami tactics instead of blitzkrieg ones.
And that's what the Social Democrats did: They didn't insist on violent revolution, they were content - at least for a time - with better wages, better working conditions, better political participations for the workers. And look where they got Western Europe! And look what FDR did for the US! Giving up two birds in the bush got them one bird in the hand. And then another one. And then another one... It allowed them to build bigger coalitions, to be accepted by people they needed as allies. In the end they achieved much more than their Communist sister movement.
Setting up a certain group of people as 'the enemy' is going to push many other groups you'll want on your side away from you. I understand that the current state of the Republican Party makes inclusive politics much harder, but maybe that's the key to breaking their strength: Eating away at their base. By emphasizing how the bible and ecological preservation can go hand in hand, by pointing out how big businesses, when not kept in check, destroy the very communities that Republicans pretend to protect... By making it easy for people to join you without radically breaking with their previous political beliefs. By reducing or eliminating the mental difficulties with switching political allegiance. By giving up some ideological purity for a lot of tangible political gain.