In a previous academic life, I spent more time dealing with and thinking about issues of copyright, intellectual property. You can avoid all that in academia pretty easily, especially if someone once told you about "fair use" and you like to use that phrase to cover the things you do with copyrighted materials in your teaching.
Fair use is a provision that allows academics to use copyrighted material without permission or payment, under some circumstances.
Some of the myths addressed in that article are probably "news" to many academics. Right up front, too many people think educators have "special privileges" when in reality they have copyright exemptions, but they are quite limited.
It scares me when teachers seem to believe that they can do whatever they want with materials because what they are doing is "noncommercial." Not true, and not a defense that will work in a court. (See the publishers’ lawsuit against Georgia State University concerning issues around library fair use)
The reality that more people (though still a minority) are sharing work for free with others uses Creative Commons licenses and other methods is probably already causing change and certainly pushing us to make real legal changes - but it hasn't happened yet.
While what you do in your classroom may be covered by Fair Use, when you post material online, present at a conference, share your slides online or in a YouTube video, you are in a very different place. The film you show to your class in room 206 is simply not the same thing as posting that film or excerpts from it in your LMS.
You'll need to go beyond this post (and others I have done on this topic) and the referenced article in order to understand Fair Use. But educators need to have those conversations and learn about what it means to say that a use is “transformative” as you will read in copyright language.