If the processor gets eaten up, disabling "Force stop" will mean a user can only uninstall the app from Google Play or Device Settings (only if Device Admin is disabled)to free up running processes as well as potential memory leakage. Mobile security solutions by default will in general adhere to disabling "Force stop" for one good reason - malware could indeed "Force stop" the virus engine, rendering the Android device vulnerable to infection.
Also, if "Force stop" or "uninstall" is disabled the security app will ask for "Device admin" (used mainly in enterprise security) - a user can deactivate Device Administration by > Settings > Security > Device Administration - uncheck box. Once this is done, you can then "Force Stop" or "Uninstall" the app as normal from Settings or the Play Store. :)