What about mom's smoking pot at home with the kids around?
You give an analogy, but use an illegal substance as a substitute for tobacco smokers. Apples and oranges, my friend. How about substituting, "Had a beer" for "smoking pot"? That frames it a little better, don't you think?
What about people that leave their kids in the car while they run into a store?
Again, not a seamless analogy. Leaving kids in a car can kill in less then an hour. Even the most agitated of the anti's don't claim that secondhand smoke can kill that swiftly or surely. Do you think we are smoking pure cyanide? I would think that that was the definition of, "totally over the top." Once again, not a worthy tactic here on FreeRepublic, where facts do matter.
What about people that slap, but not too hard, their child in the face?
If you think that breathing smoke is the same a a blow to the head, than I'm afraid you have some trouble descerning reality on this planet.
I've intervened in all of the above.
In the first two situations, as you describe them, I would probably agree with your actions. (Did you call the police, or just speak to the people involved?) I would need to know more about the third. (N)ot too hard, means...not too hard, so why would you feel compelled to intervene?
Do you have some expertice in this area?
Do you know the total situation better than the parent?
Or do you just like to throw your weight around?
From the tone of your posts, I would guess the latter.