Economists clueless on macreconimic issues?

I recently read a post here that stated basically that economists start talking about the psychology of the people but don't understand psychology and that at the macro level economists are pretty much clueless. Take a look at the article. It is a good read as well as many of the comments.

One of the major problems with economics is that it is really difficult to test macro level theories. How do you run a randomized experiment on some theory at the national or global level? You don't. No politician will let you use his/her people as guinea pigs. We don't want to be guinea pigs. Yet we have learned that good data is much more reliable than intuition and gut feel (see these slides and this book).

The only way to understand macroeconomics reliably is with experimentation (like all other good sciences) and that is near impossible at the macro level.