Let's say you had a time machine that would take you to some random point during the last 40 million years? How should you dress? On average, this photo represents a warm and balmy day on during the current ice age, which, over the last 40 million years, has seen long periods of glaciation sporadically broken by short warming periods. Now, are people better off with the temperatures we know of from recorded history, or would it be better if world climate was simply stuck at its average point? The question answers itself: there is a reason that recorded history coincides with warm weather. But if we are the beneficiaries of past warming, why do we assume that the next warming period will be catastrophically bad?
[Note: This post has been changed slightly to conform to the facts.]