Activist investing is kind of pointless in that an efficient market reallocates funds around it. Like, if an investor chooses not to invest in X for some sort of reason other than the expected value of X, it reduces the value of X, sure -- but also creates an incentive for others to invest in X. The actions of other investors are not independent of the actions of the activist investor.
I once heard it described as trying to "bail a hole in a lake." New water goes right back into the spot where it was taken from.