Linux is a shared playroom, and thus needs to make most players reasonably happy. LSM thus needs to meet two criteria: be relatively painless for people who don't want it, and be useful and effective for people who do want it.
We feel that LSM meets these criteria. The patch is relatively small, and the performance data in Section 4 shows that the LSM patch imposes nearly zero overhead. The broad suite of security products from around the world that have been implemented for LSM shows that the LSM API is useful and effective for developing Linux security enhancements.