We've perhaps all heard this argument:
Non-abortifacient contraception is fine because if it's God's will for you to have a baby he'll just see to it that the contraception doesn't work.
This argument is wrong on so many levels that it is hard to begin assessing them all: Calvinist assertion of inviolability of God's will, begging the question, putting the Lord your God to the test, basic stupidity, etc.
So, I'd like to ask for further exposition of everything that is wrong with this statement. And, more importantly, what would be the best pastoral response to such an erroneous assertion?