I agree, it should be understood that whatever optional activity Avast might perform the option to enable or disable that option should be available to the user, in the event the option is unavailable as a result of something that is not install then the activity should by default not occur in that circumstance.
Put simply: If an option to change an optional action by Avast is not available then the action should not occur by default. This is not only common courtesy but common sense.