When a vendor requires an email address to access a whitepaper, it's a scam designed to harvest email addresses for marketing purposes. I've been down this route with my own marketing departments, criticizing them for this.
Yes, ASKING for an email address is appropriate. Some want to receive data this way. REQUIRING an email address, though, is a well-known technique designed to harvest personal information.
I certainly erred here, treating a stranger differently on the issue than I've treated friends (and indeed, my own company) when it's happened in the past. But the fact remains is that people who harvest email addresses this way should be criticized.
Conversely, you shouldn't be defending your friend's harvesting email addresses by saying it's not wrong, you should be agreeing "dude, yea, stop harvesting email addresses, and provide the content without requiring an email address".
