I see your point & I'm kind of in the middle on this.
I set my Avast up with "Ask" & "No Action" .
If it was set to "Fix Automatically" then a false positive might be a problem.
So it depends on the user.
Also I get very few false positives .
I know one software that Avast always finds a false positive of sorts on . That is PGCEdit. It give several "Error: Archive is password protected ." files . I know this & ignore it.
I've never had Avast find a system file as a false positive.
This thread is about Avast & Windows 8.1 . I don't have Windows 8.1 & it could be more of a problem for it.
I also have a second AV installed but inactive . So no conflicts occur .
I can scan a file of folder with it this way . It is Emsisoft Anti-Malware .
I usually use the "Disable the shields for 10 minutes" option in Avast when I do that.