Over the years that we have produced e-commerce software, some customers have queried the need for the extra confirmation step, as they feel it reduces the number of sign-ups on the list. While it does indeed do this, the reason is clear: to prevent the addition of addresses by people who don't own those addresses (either accidentally or maliciously).

For example, I could sign up an email address of someone with a very similar email address to mine by accident. But I would not then receive the confirmation link, and so could not click it to confirm the address. Consequently, this bad address would not be added to the mailing list.

Your web host will not tolerate you continuing to mail to a list which has generated spam complaints because some addresses turn out to belong to people who were added without their consent, especially once they find it is because you did not confirm addresses properly. In such cases, the whole list is tainted. While 99% of the addresses might be genuine, you have no way of knowing which ones are not, and will have no choice but to discard the whole list and start again using proper opt-in confirmation.

So there is nothing to be gained from not using opt-in confirmation, because it is only a matter of time before you'd be forced to discard a tainted list and start from scratch with it.