Is your email address public?

I had an interesting (!) conversation with a guy that I had just met last week. We were talking about email marketing and I have to admit up front that he irked me.
Why I hear you say? Because I’m normally so mild-mannered.
I’ll tell you why.
He emails about 8,000 people on a monthly basis. He said that “a girl in the office” got the local directories, golden pages and started inputting details into a spreadsheet which later became the email database.
I practically jumped off the chair and said ‘no way!’. He argued that if your email address was in the public domain, then surely it’s okay to send a mail.
I informed him of the Data Commissioner (He typically emails Irish businesses) and said there is a law against that. He said ‘yeah but is it really the law?’.
So I won’t tell you what I said to him, (I’m too polite on this Tuesday morning!). So I’m looking to you to help me out.
I’m meeting him again this Thursday and I promise to be more composed. I have my own ideas but that would bias the conversation.
Can you help me to help him? If you were me, what advice would you give him when you see on Thursday?