There have been so many scientific and technological advances during the last 1,000 years that even listing them would be a massive undertaking. One can scarcely imagine what the life of an average human (one who hasn't been raptured) will look like 1,000 years from now, except that the peak of today's science and technology will undoubtedly appear quite primitive. And yet, our modern science and the technology it has made possible could be 1,000 years ahead of where it is now if not for the aptly named Dark Ages.
As my readers almost certainly know, the Dark Ages refers to a period of roughly 1,000 years during which the science of the ancient Greek and Roman societies was forgotten, discouraged, and suppressed by medieval Christians. By placing their "holy" book above all else and fighting anything that was not consistent with it (e.g., reality), early Christians set back scientific progress approximately 1,000 years.
What is even more troublesome than losing the advances of the ancients to early Christians' war on reality is that there are Christians today working toward similar ends. The Dark Ages isn't just a bad chapter in the history of Christianity; similar efforts by Christians to suppress science are ongoing. Recall that opposition to modernism and anti-intellectualism are key components of Christian extremism. The result is that we have a politically influential movement in the United States opposing public education, battling science, and working to prevent equality for women, LGBT persons, atheists, and many other groups.
The next time someone asks you what is so bad about religion, don't forget to mention that religion has done far more than delay scientific progress. I also hope you'll note that, even today, religious extremists are trying to undo centuries of scientific progress. They are holding us back to our collective detriment.
