After all, linear econometric models are based on linear multivariate functions which get extrapolated get out-of-sample forecasts. Extrapolation is bad only if the underlying econometric model is fragile or based on flimsy theory. Otherwise, extrapolation can work pretty well locally if based on a credible model.
But agree with you in part that the entire area of economic forecasting is not science. At best, it's only partly science. The rest is some combination of data mining, judgement, leaps of faith, and common sense...