Maybe I can field some of these:
Correct. That's the entire basis of the soapbox.
Well, if we are really going to try to shoehorn this example in, it would be more apt to say that if you hit your own kids, that preaching against raping your own kids would be untenable.
There's a few different angles here. If you complain that hardcore drug takers can't control their addiction, that would be untenable as you have an addiction.
This is a great example, worthy of its own soapbox, but there are many pro-alcohol, anti-drug people all over the world. Alcohol is one of the most debilitating, violence inducing drugs, and it's the legal one.