if you were king of westeros and you wanted to completely and utterly remove the ironborns raiding, how would you go about it? is there any possible way of stopping it short of killing every man woman and child on the isles?

I think there’s a subtler and more effective way of doing this: support the New Way over the Old Way. The thing that people get wrong about the Ironborn is they think that Ironborn culture is equivalent to the Old Way, when there’s a long-running cultural conflict between the Old and New Ways. 

So what I would do is support Lords Paramount like the Hoares or Vickon or Quellon Greyjoy, and lesser Lords like the Reader, whether that’s financial support or other kinds of resources (maesters, books, septons, etc.) or royal offices and the like. Build up a popular coalition in favor of the New Way who can stand up to would-be Shrikes like Aeron and would-be Red Krakens like Euron.