>First, my problem is that justification by reference to an ideal state of
>affairs will fail to motivate people in the here and now, where conditions
>are not ideal.
The rejoinder would be, we always already presuppose this ideal, or some such approximation of this idea, whenever we speak. The ideal does not motivate, it is the equivalent, I think, of a Kantian postulate. What motivates people are their interests: self-preservation, desire, emotions, feelings, affections, reasons and so on. Habermas argues we can distinguish between two kinds of interests: an interest in understanding and an interest in mastery. One is practical, the other is technical. It is our interest in these two things that motivate us to learn, not the idealizations that we make. The idealizations, in effect, are the simple 'assumption' that when we try to understand or mastery something, we assume that it is possible.
I think this is the clearest formulation that I've been able to come up with.
ken