Sometimes discussing theory doesn't give me the "flavor" of the situation. In the drowning scenario, let's do this:
Scenario one: A total stranger is drowning.
Scenario two: Your child is drowning.
You don't swim very well and the water is turbulent, so there is a good chance you may drown too if you jump in to rescue the victim.
Examine your mind states in these scenarios. I'll be honest. If it were my child there would be no thought at all; I'd jump in without hesitation. If it were a stranger I'd still probably jump in but there would be a moment of "Oh crap, what am I doing?" right before.
In the second scenario I guess it could be argued I replaced an unwholesome mindstate (fear, hesitation) with a wholesome mindstate.
Now what if you recognize the drowning person as a recently-escaped rapist/murderer/arsonist/terrorist? Would you decide, "kamma. Screw him."
Or dive in and drag him out.