As already mentioned several times, disabling shields (or equivalent of other security tools), or disabling services, or disabling drivers, may not be enough. That's the reason for the specific removal utilities for each security tool.
Just to give an example, Avast has context menu additions, a screen saver, a localhost, an SSL module, several shields (not completely independent from each other), a service, a driver, and possible more.
If a user would "try" to "disable" Avast (so to use an additional resident security tool instead), how many interconnected items and settings would be really needed so to neutralize any possible interference with that other security tool?
Each update of Avast (usually twice a day) can change the engine and the virus definitions. To that, add a recent program update, which included also new settings that were not there before.
Some security tools are designed to be non-resident scanners or alike. Usually (but probably not always), Avast will work correctly together with those. Certainly with resident security tools Avast might find some conflicts, if not in some version, then maybe in the next.
Use only one resident security tool, and run the respective removal utilities for the others you ever had.
