Email Marketing - list purchases

There is some debate about whether or not to purchase an email list to market to. I take the opinion that if you don't know the person or if they have not given you permission to email to them then DON'T.

Some services (I use Constant Contact) have rules against using purchased lists. It is against their policy to email to anyone without their permission and they will ask you that specific question about the list you are importing. Here are some things to consider:

1. Do you want to be considered a spammer? Whether you are, or not, your email might be considered spam.
2. Do you reply, purchase or even read email from places that you don't know? I don't, instantly deleted. Which makes the purchase of a list a waste of money.
   
3. What kind of message does it send about your company that you send unsolicited email?
4. Many times you don't own the list, it is sent out for you by a 3rd party.
   

The case could be made that yes, this type of email marketing works and you could increase your sales. But at what expense?

Your feedback is appreciated.