This misunderstanding results from an inadequate comprehension of what God actually does in entire sanctification. Because of a new orientation of the heart, it is possible to live above willful sin. However, no intelligent proponent of entire sanctification would argue that sin becomes impossible. It is possible to not sin. But to commit sin is not impossible.
Security is a relative matter.
For instance, I am sitting on a chair as I type these words. Unless I am overtaken by dizziness or other severe sickness, my changes of falling out of this chair are slight. If the chair is placed on top of a table as I stand on it, my security is further jeopardized. Preposterous as it would be, if I were to stand on the chair while it is perched in the towering tree outside my window, I would be much less secure than sitting here in my office. So it is with the security of believers.