The Problem of Universals, Abstract Objects, and Generalizations in Politics You have to plenty believe in universals and abstracts to follow up something like socialism. It is a political basis that only exists in abstraction of ideas, but it has never been applied practically. Even those nations which considered themselves as socialists hardly maintained the praxis with the pass of the years. Something like "common ownership" cannot be applied to subjects, because it is absorbed by the collective itself and disappears into the mass. So no, their politics are not concerned with something apart from their ideas and dreams.
I think the question isn't discerned in Platonic nor conceptualist, but over socialization. A person is said to be well socialized if he believes in and obeys the moral code of his society and fits in well as a functioning part of that society. Even though he doesn't understand the conceptualisation. The collective tells you what to think and how to be a good neighbour, easy. They generalise the behaviour and the basic values of society. Generally speaking, the goals of today’s socialists are not in conflict with the accepted morality. On the contrary, the left takes an accepted moral principle, adopts it as its own, and then accuses mainstream society of violating that principle. More fundamentally, the duty of the individual to serve society and the duty of society to take care of the individual.
I agree with unabomber when he explained in his manifesto: One of the most important means by which our society socializes children is by making them feel ashamed of behavior or speech that is contrary to society’s expectations. If this is overdone, or if a particular child is especially susceptible to such feelings, he ends by feeling ashamed of himself.
My intention is not to go off the topic of your post, but I fully recommend a look on Unabomber's manifesto: Industrial society and its future, You may find some related points to your arguments, and maybe you will consider them useful.