I have provided answers for both this example and the one I gave in the related topic about legality. In each case, I've taken a completely different approach for a couple of points:
On my example, giving the internet a method to scrape all the video from a site meant one thing: if more than a couple of people wanted to do it, it was going to cost the owner of the website a ton of money. All because of a mangy little answer I had written. I could have given the answer but I chose not to.
By the same reasoning, harvesting emails harms nobody. Email is public information. You can attempt to deny that but hiding your email indefinitely is an exercise in frustration. It's going to come out eventually and as soon as it does, you're automatically on every spam list. One guy harvesting emails that are already in the public domain is going to have a net-0 effect on the amount of spam they get, even if he does decide to send them spam.
However, being able to scrape a site and pull information from it is a transferable skill with legitimate and useful analogues. On balance, sharing a solution is a positive thing, I think.
I've picked a moral line in there somewhere and I'm following it for now. I'm sure future examples will help to blur it as people become more creative in ways to be evil.