You would not think that is you or someone you cared about needed a new organ.
> how do you prevent your liver from going to an alchoholic who likes to fuck children?
Er, I think the 1 in x00,000 chance of my organs helping someone like that is a risk worth taking for the much much higher chance they will help decent people.
There is nothing that I can do to stop my organs being donated to people who say dickish things on the Internet like you just have either - and if there were processes available by which I could express a preference there are a lot of people who would jump the queue in front of you should you be needing and otherwise next in line at the time.
You could use exactly the same ludicrous argument to "defend" never giving anything to any charity or other cause.
I'd imagine that particular combination is reasonably rare, and most donation organizations require alcoholics to demonstrate abstinence from alcohol for 6+ months to be eligible.
Demand to control your organs and what they are used for.