Or perhaps: "To say that legislation can bring about an end to murder is akin to saying that someone's fever could be cured by dousing his thermometer in ice."

Right or wrong, the sentiment has no bearing on whether something should be legislated upon.

Was not child labor ended (or significantly reduced) by improved economic conditions at the latter end of the industrial revolution enabling parents to earn sufficient income such that they did not need to send their kiddies off to the sweat shop?

No James, child labor ended when an education in the present became more valuable that earning wages in the present, taking into account the difference between educated labor later and uneducated labor for the rest of you life, discounted for the time value of money.

Basically, before Social Security and 401k plans parents had kids as a retirement plan. An education for their children became a better investment for the parents personally.

Child labor still exists even the west, we call it "chores".

BTW, I met Thomas Woods this past week at the Austrian Scholars Conference. He gave a great talk on the economic fallacies of Catholic social teaching.