You can still draw causal links, in the same way we don't need quantum physics to understand laws of motion of large bodies. Was Newtonian physics lacking micro foundations?

There was quite a bit of this back and forth with Krugman, Noah Smith and the gang over micro foundations over the last few years. Maybe we can agree that micro foundations improve the model, but aren't necessary nor sufficient. Especially when micro foundations are pieced together to give the macro results.

Here is Simon Wren Lewis on it

Suppose there is in fact more than one valid microfoundation for a particular aggregate model. In other words, there is not just one, but perhaps a variety of particular worlds which would lead to this set of aggregate macro relationships. (We could use an analogy, and say that these microfoundations were observationally equivalent in aggregate terms.) Furthermore, suppose that more than one of these particular worlds was a reasonable representation of reality. (Among this set of worlds, we cannot claim that one particular model represents the real world and the others do not.) It would seem to me that in this case the aggregate model derived from these different worlds has some utility beyond just one of these microfounded models. It is robust to alternative microfoundations.

Lastly, I'll add this classic post of Krugman on the subject http://krugman.blogs.nytimes.com/2012/03/02/the-microfoundation-thing-wonkish/

Mark Thoma sends us to Simon Wren-Lewis on microfounded macro models (especially the DSGE models that have dominated the literature even on the Keynesian side) versus “ad hoc” models like IS-LM. Wren-Lewis is on my side, sort of; but I’d like to add a few points, in no particular order.

1. Even in microeconomics, we don’t insist on using models built up from maximizing behavior all the time. Exhibit A: supply and demand! I mean, we kind of know how something like the supply and demand curves can be derived from maximizing behavior, but it’s not all that easy, and nobody, nobody, insists that you do this derivation every time.

2. Relatedly, as a practical matter intellectual scratch-pads — approximate version of what we really believe, but stripped down to be tractable — are what one uses for applied economic analysis all the time.If I want to ask what the effects of some shock will be, it rarely makes sense to demand that the analysis always go all the way back to the intertemporal choices of optimizing agents.

3. In the hard sciences, when dealing with complex systems people have often used higher-level, aggregative concepts that seem to work empirically long before they have a full derivation of effects from the underlying laws of physics. Read Air Apparent, a nifty book on the history of meteorology: meteorologists were using concepts like cold and warm fronts long before they had computational weather models, because those concepts seemed to make sense and to work. Why, then, do some economists think that concepts like the IS curve or the multiplier are illegitimate because they aren’t necessarily grounded in optimization from the ground up?

4. And when making such comparisons between economics and physical science, there’s yet another point: what we call “microfoundations” are not like physical laws. Heck, they’re not even true. Maximizing consumers are just a metaphor, possibly useful in making sense of behavior, but possibly not. The metaphors we use for microfoundations have no claim to be regarded as representing a higher order of truth than the ad hoc aggregate metaphors we use in IS-LM or whatever; in fact, we have much more supportive evidence for Keynesian macro than we do for standard micro.

5. A practical observation: the economists who get most bent out of shape at the notion that maybe we don’t always have to derive everything from optimizing individual agents also tend, with remarkable regularity, to be the economists who make simple, ludicrous conceptual errors when they discuss real-world macroeconomic issues. See many posts here and on Brad DeLong’s blog for examples. I don’t think this is an accident; it really helps your ability to think clearly to have those simplified, ad hoc models always in the back of your mind.

In these circumstances, it would seem sensible to go straight to the aggregate model, and ignore microfoundations...