Jonathan Chait devotes a long article to arguing that liberals are pragmatic and empirical.
The contrast between economic liberalism and economic conservatism, then, ultimately lies not only in different values or preferences but in different epistemologies. Liberalism is a more deeply pragmatic governing philosophy--more open to change, more receptive to empiricism, and ultimately better at producing policies that improve the human condition--than conservatism.
That explains why liberals are leading supporters of experiments with school vouchers.
It is interesting that a famous book by Thomas Sowell, The Vision of the Anointed, is dedicated to the converse proposition. Sowell argues that statist solutions are endorsed by liberals despite their manifest failure. He argues that it is liberals who are impervious to empirical data.
For Discussion. Over the past 50 years, what is the most significant example of (a) mainstream liberal opinion changing in response to facts; (b) mainstream liberal opinion failing to change in response to facts; (c) mainstream conservative opinion changing in response to facts; and (d) mainstream conservative opinion failing to change in response to facts?