From <PERSON>'s answer: "In <PERSON>'s contemporary context, they're obviously the mills of the Industrial Revolution"
Hardly.
In 1804 there were no mill towns and very few mills in towns: the image conjured up in the popular imagination by the expression "Dark Satanic Mills", of tens of factories belching out smoke and turning the sky dark, is not one any human being would even have imagined in 1804. Such landscapes only started to appear circa 1840s.
<PERSON> and others built coal-powered mills starting in the 1770s. These were not the first powered mills: mills powered by rivers, wind or animals had existed for centuries. Invariably the new coal-powered variety were stand-alone "plants" built in the countryside, particularly close to canals so that large quantities of coal could be delivered to them cheaply - roads at the time were few and usually just dirt tracks, and the canals were a crucial factor in ushering in the industrial revolution, a kind of superhighway between coal mines, the new powered mills and the hubs of production of raw materials and of consumption.
These coal-powered mills were surrounded by countryside. 736
Working conditions were generally better than in the later intense phase of the industrial revolution, and wages were much better than for hard and unhealthy agricultural work.
By "Dark Satanic Mills" <PERSON> thus unquestionably means the churches of the Established Church (Church of England). They were "dark" and "satanic" because, as <PERSON> saw it, their primary function was to suppress the natural cravings for truth and freedom of the ordinary people whose lives they blighted, with "mind-forged manacles".
This is a powerful expression, precisely because of the metaphor of mills: by 1804 someone like <PERSON> would have been able to observe the new industrial mills in operation. It is important to understand that there is no evidence for explicit or even implicit criticism of the industrial culture they were to usher in in <PERSON>'s writing: he did not foresee this. Most people lived a precarious hand-to-mouth existence in the fields in Britain then, working very long and hard days and enlisting the labour of small children at times of intense agricultural activity: similar working conditions in the mills did not single out the mills as uniquely egregious. Life for most people was egregious.
What <PERSON> did observe, however, is that mills churned out vast quantities of products, all of them alike, and this is the force of the metaphor: churches similarly churned out souls, stripped, as he sees it, of the aspirations and individuality which are human beings' spiritual birthright. 736