STOP FORCING US TO OPT IN AND CONFIRM BEFORE YOU GIVE US THE DAMN PRODUCT WE JUST PAID YOU FOR!!!
It's completely unethical and all it does is make me want to do a 'spite chargeback' or sign YOU up to about 50 obnoxious lists and make you wade through the confirmation emails.
At the very least, make it totally plain ON YOUR FREAKING SALES PAGE that your price is not simply the money you're asking for, but also my contact info. Because that is a form of payment, too.
Making me opt in to your list to get what I just paid you money for makes me instantly suspicious of whatever you just sold me, and I'm just going to unsubscribe immediately anyway. So all you've accomplished is the assurance that I'll never buy anything from you again, and you won't be able to try to sell me anything via emails.
Good job, dumba**.