[C19fan]

There are different interpretations of the term. The obvious one as you cited is a referral to the new industrial factories. Blake wasn’t the only one who considered them a blight on the land. Some believe Blake was referring to the corrupt Church of England. As this Wikiepdia entry cites Blake and many others in the Romantic movement were rebelling against the dominance of reason from the Enlightenment period.

[C19fan]

https://en.wikipedia.org/wiki/And_did_those_feet_in_ancient_time

[sparklite2]

rebelling against the dominance of reason from the Enlightenment period.

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Thank heaven we’re beyond that now. /s