Usually the value of "0" is off and "1" is on.
Yeah, mine is set to "0" in dvars but the default value is "1". I kinda doubt that'll disable VAC though.
VALVe will not ban its customers for single player usage regardless of what you put into the SP mode, trainers, dev console cheats, etc.
Then how come VAC2 is activated in Singleplayer?