Why do atheists argue that religion slowed social and scientific progress during the middle ages?

Because the catholic church actively repressed science that threatened its influence. I agree that humans will always be able to form dogmatic institutions, but I think the key was the fact that religion had political power in the Middle Ages. I think you're right, authoritarianism is the main culprit however the idea that the ruler is in connection with the ultimate creator of the universe and holds the key to the salvation of the masses certainly helps.

The Greeks were doing just fine without you. They not only knew the Earth was round, they knew how far it was around it.

It took 1400 years under your religion to get back to the point that it was.

I agree that there is a LOT more to it than merely religion/not religion -- that kind of mindset is simplistic.

That said, the rate of technological progress in Europe increased during the pre-Christian empire, and did a major back-slide, especially in the west, after the Papacy started to dominate the western Empire's culture.

Similarly, during the Renaissance, when curiosity began to flourish again, in no small part because of an increased availability of pre-christian reading material, the Christian church went out of its way to judge new discoveries against how they personally interpreted the bible -- including burning research and jailing & killing researchers.

So yes, there was more to it than JUST religion (climate cool-down, famines, invasion, crop failures), but religion did intentionally interfere with progress for the space of a few centuries.

In view that it did. Seem at the historical Romans or in special the Greeks. They made fine scientific advancements. Sure they still engaged in war and even owned slaves but they didn't oppress free enquiry. Then after Christianity came along to fill the void left by using the Roman Empire, nothing for the subsequent thousand years. That's why it used to be known as the darkish a long time. A stagnant, static millennium long theocracy. You will see this even turbo (and still occurring at present) within the core East. For about the first 300 years of it is existence, Islam was very open to scientific advancement. What's now Baghdad used to be a town with many spoken languages, specific religions and those of none and they made high-quality advancements. They invented algebra ("algebra" is an Arabic word), made pleasant strikes in physics, treatment, astronomy (they may have invented the telescope 600 years before Galileo). Then within the eleventh century, they threw all of it away. For explicitly religious causes. They underwent a sort of reversal and destroyed all of their scientific competencies which plunged them into a black gap which a thousand years later they have got yet to dig themselves out of. Every 12 months the whole Arabic talking world (a couple of billion individuals) publishes lower than zero.01% of academic publications. Spain interprets more books into Spanish every 12 months than the entire core east has, ever. Why argue that religion has slowed social and scientific development considering it has. Find it irresistible or now not those are the data. In case you wanted to suppose up a "growth retardant" you couldn't do any higher than faith.

Personally, I don't make that argument, since I do not know enough about the period to know whether it is true. Of course some religions have done or are doing their best to oppose science by advocating ideas such as Geocentricism or Creationism.

It's a simplistic argument. More nuance would reveal that the scientific method was a product of church thinkers, including Aquinas, Occam, and Gassendi. The problem is that once scientific method was formulated, the old "revealed" claims continued to hold undue influence, and even leading to the imprisonment, torture and killing of many great scientific thinkers. That certainly slowed scientific progress. So, the issue is that at its advent in Europe Christianity was progress, but it soon outlived it's usefulness, and has long since been obsolete.