I think my google skills are failing me. I’ve long held similar, if not identical, views to Justice Douglas and I’ve gone down a frustrating First Amendment rabbit hole so I’m looking for some sort of guiding light. In Miller he wrote “Obscenity — which even we cannot define with precision — is a hodge-podge,” he concluded. But I have no idea if there’s something in his many books or a lesser known opinion.
Any help would be appreciated. Thanks guys!
Anything I find in a quick googling is that Douglas did not believe any restrictions were permissible, and so he had no need to define a line for what was not.
As it happens, I’m now reading Noah Feldman’s Scorpions, a pretty good book about four of FDR’s appointees to SCOTUS, including Justice Douglas.
It was Justice Potter Stewart who uttered the famous line, “I know it when I see it.”
Right, it was Potter Stewart. And oddly enough, it’s usually LIBERALS who mock him for saying that. Which is odd, because Stewart was generally very supportive of freedom of expression. He ruled in FAVOR of Louis Malle, whose movie “The Lovers” was accused of being obscene. Stewart was saying, in effect, “I know obscenity when I see it, and so does anyone with any common sense. And Louis Malle’s movie is NOT obscene.”
Mark Twain said “a dog is that which is recognized as a dog by other dogs”.
So similarly, pornography would be that which is recognized as pornography by people who know pornography.
(Or - smut is in the eye of the beholder)
It’s possible that Stewart was as right as it’s possible to be, and that his somewhat offhand-sounding remark might be oddly definitive: I think an explanation that obscenity is inherently a moving target is a necessary part of any true definition of the word.
Radicals go further, saying that “a moving target” is not only necessary for defining obscenity, but also sufficient. 
This doesn’t cover it, because people who know pornography now would disagree with people who knew pornography in the 1600s.
The National Lampoon once (mis)quoted Chief Justice Rehnquist as saying, “Pornography is whatever makes my robes rise.”
If we’re piling in with non-judicial obiter dicta, there is a saying that erotica is what you do with a feather, pornography is what you do with the whole plucked chicken.
Well, yes, tastes change over time - hence the need at one time for glue-on fig leaves.