The purpose of security is generally to prevent people from using computers and computing resources in ways that are not authorized by the owners/administrators of said computers.

The purpose of copyright is to restrict people from using documents in ways not authorized by the author or current copyright owner of said document.

The significant difference is the question of whether the owner of a machine is allowed to use the machine and data on that machine as they intended. The goal of the SSSCA was to answer this in the negative. My objections were to the fact that the SSSCA prevented people from choosing how they wanted to work with their own computers.

Cheers,
Ben