Every day Americans receive UCE – unsolicited commercial email – .i.e. SPAM, that they aren't interested in and didn't sign up for. Some malicious individuals even sign others up to receive UCE–the 21st Century equivalent of a crank phone call. Unscrupulous emailers also often embed unsubscribe links in a linked image file which is often not immediately downloaded by popular mail reader software. Downloading the image to unsubscribe gives the spammer confirmation the email was viewed.
In contrast, good emailers send a confirmation email to verify that the recipient really wants to receive email from them before continuing.
The CAN-SPAM needs to be amended to require two things: first require an opt-in confirmation, and second, provide a plain-text opt-out link at the start of the email.