One thing I've noticed in this is that some people are firmly convinced that Firefly fans making and selling Jayne hats is illegal. Considering the nature of Firefly, fans are probably more concerned with right and wrong than legal and illegal. I'm going to set aside the complex issue of right and wrong here, and talk about whether it is legal or illegal . . . which is really no less a complex issue.
Part of why it is a complex issue is that copyright on clothing is much looser than copyright on most other things, and for good reason. A lot of clothing is very similar to serve similar basic functions, so overly strict copyright would result in things like Levi having a monopoly on blue jeans. Here is a good general article on clothing copyright. So, the Jayne hat is not a good candidate for being copyrighted, trademarked, or patented. It is a very basic classic hat pattern, the earflap hat with a pom-pom. Yes, it has a specific color arrangement to it, but that isn't unique enough to change anything legally. It is a pattern that is very easy for a knowledgeable knitter to recreate from a photo. Fox may have legal precedent to take issue with the marketing methods of people selling Jayne hats, but not so much the making and selling of hats in and of itself. And, in fact, many Jayne hat-makers are renaming their hats and changing the language and images of their marketing to get around this.
I'm going to tell you what Fox should have done if they wanted to keep some control of the knitting of copies of the hat, which was designed and knitted by a production coordinator on Firefly who based it off a watercolor sketch by the costume designer. They should have published and sold a pattern, with standard knitting-pattern restrictions* on distributing the pattern, selling items mades from it, etc. Ideally they would have done this as long ago as possible, back when they first got the inkling that fans would want to knit this hat. A pattern can be copyrighted. Knitters are used to seeing restrictions on the use of a pattern and the items made from it. There would be more understanding of the idea that it reasonably okay to accept money from your friend to knit him a hat from a pattern he purchased for that purpose, but it isn't cool to knit a ton of them and sell them.
If there had been a pattern published, knitters wouldn't have had to create their own patterns, and if they had their hats would truly be seen as knock-offs by people who didn't want to pay for the pattern. But without that official pattern, it was inevitable that knitters would do the simple work of recreating the hat they'd seen on the show, then share their patterns with others on the internet, considering it to be their own work. Then others knit hats from those pattern, seeing no restrictions to what they should do with it. The Jayne hat trend grew and grew until there were large operations making and selling the hats. And then, much too late, Fox decided to do something about it, and handled it poorly.
Even with a copyrighted pattern published for the hat with restrictions on its use, the legality of enforcing those restrictions is still fuzzy*. But it would still be a much clearer situation giving guidelines to knitters to do the right thing.
*Here are two good articles on knitting pattern copyright: