Economists often make unrealistic assumptions but so do physicists, and for good reasons. Physicists will describe motion on frictionless plains or gravity in a world without air resistance. Not because anyone believes that the world is frictionless and airless, but because it is too difficult to study everything at once. A simplifying model eliminates confounding factors and focuses on a particular issue of interest. This is as legitimate a method in economics as in physics.
Since there are easy responses to these common criticisms of bad predictions and unrealistic assumptions, attacks on the profession are ignored by professional academic economists, who complain that the critics do not understand what economists really do.
But if the critics did understand what economists really do, public criticism might be more severe yet.
Even if sharp predictions of individual economic outcomes are rarely possible, it should be possible to describe the general character of economic events, the ways in which these events are likely to develop, the broad nature of policy options and their consequences. It should be possible to call on a broad consensus on the interpretation of empirical data to support such analysis. This is very far from being the case.
The two branches of economics most relevant to the recent crisis are macroeconomics and financial economics. Macroeconomics deals with growth and business cycles. Its dominant paradigm is known as "dynamic stochastic general equilibrium" (thankfully abbreviated to DSGE) - a complex model structure that seeks to incorporate, in a single framework, time, risk and the need to take account of the behaviour of many different companies and households.
Economics is not a technique in search of problems but a set of problems in need of solution. Such problems are varied and the solutions will inevitably be eclectic. Such pragmatic thinking requires not just deductive logic but an understanding of the processes of belief formation, of anthropology, psychology and organisational behaviour, and meticulous observation of what people, businesses and governments do.
The belief that models are not just useful tools but are capable of yielding comprehensive and universal descriptions of the world blinded proponents to realities that had been staring them in the face. That blindness made a big contribution to our present crisis, and conditions our confused responses to it. Economists - in government agencies as well as universities - were obsessively playing Grand Theft Auto while the world around them was falling apart.