The actual effects of government intervention and their intended effects

They just don’t get it. Why do they think “the siren song of collectivist solutions” is going to make things better? There is no empirical evidence either specifically (for example, here or here) or generally to support them. Their wandingerous arguments mainly consist of flippant remarks and personal insults.
I think Milton Friedman best sums up John’s points (subscription) in Capitalism and Freedom:
“…conditions have changed. We now have several decades of experience with government intervention. It is no longer necessary to compare the market as it actually operates and government intervention as it ideally might operate. We can compare the actual to the actual. If we do so, it is clear that the difference between the actual operation of the market and its ideal operation – great though it undoubtedly is – is as nothing compared to the difference between the actual effects of government intervention and their intended effects.”
—Milton Friedman, 1962
Whether it be light rail, pre-K or all the other past and current interventions of government, why do they think the actual effects are going to be anywhere near their indended effects. Aren’t they just engaging in wishful thinking?