Precisely.

Also, it is a well-known fact that most spammers' opt-out mechanisms are fake. By replying to a spammer, or clicking on their link, you confirm that your address is live. Instead of getting less spam you will get more spam because the existing spammer will continue to spam you and he will also sell your address to others as he has confirmation that it is a live address.

I'm not saying that IB - were they provide a VALID opt-out address - would engage in this type of abuse. What I'm saying is that people who are savvy about spam will not normally click on opt-out links, for the reason just stated.

Mailing lists should be opt-in, not opt-out - ALWAYS. I would not have objected too much to an email from IB saying "Please reply to this email if you don't mind being spammed by us", but spamming without permission is wrong.