I've stated before that I view software freedom more than a matter of licenses (and as a bare minimum). This is what leads me to say DRM is definitionally opposed to software freedom.
When I state such opinions often someone will show up & say "But you can license the DRM e.g. GPL, and use special hardware to prevent the user from modifying it to allow piracy." No. Stop right there. Preventing modification is what I mean by definitionally opposed to software freedom!
DRM is a tough knot...