"protect" is a biased term. One person's "protect" is another's "control". You mentioned "access control"; however, copyright has nothing to do with access control. Copyright is not an unlimited right to control all possible uses of a work; DMCA 1201 turns it into one, by enshrining whatever access control restrictions a piece of software implements into law.

Ignoring fair use for a moment (which DMCA 1201 also breaks, so that's another problem), copyright restricts copying. DMCA 1201 produces a restriction on usage, which copyright does not control.

DMCA 1201 doesn't actually prevent you from copying a DVD, for instance. DMCA 1201 prevents you from reading and playing a DVD using anything other than software approved by the author of the DVD.