Why do secularists heavily criticize the Middle Ages?

Oh, you mean the dark ages! That time when the church stifled all scientific progress and contributed to a feudal system which crushed the majority of the population with extreme poverty and concentrated all power into the hands of a few aristocrats. Yeah, life was grand in the dark ages, when the average life expectancy was about 35-40, medicine was nonexistant (I mean, who would need modern medicine when you can just pray to you magical sky-friend for a miracle cure?) and war and plague killed tens of thousands every year. Good times.