I understand what you are saying, and I agree that people should not be bombarded with spam because they left a comment, but let's take a look at the problem from the other point of view for a moment. How many people leave random, rude, or off-topic comments simply because they are not required to be identified? Being anonymous on the internet appears to make people think they can behave or say anything they want. I may encourage comments on specific posts, but I reserve the right to approve them before they appear on my website. Also, if they have to leave their email address in order to comment, I think they've already given me (the website owner) tacit agreement to personally contact them, should I deem in necessary.

Yes, I know that is not the same thing as harvesting emails ... but perhaps the areas is more gray to me than black and white.