XF 1.4 How to Add Newsletter Field On Registration

I'm trying to increase our email newsletter and I figured that one good way would be to add people when they first register while also giving them the option to opt-out. Obviously having the field pre-checked is preferred, but I'm wondering if it's possible to do something like this as the Custom User field doesn't seem to be the way since it's not a characteristic that someone would want publicly shown on their profile page, although I could be wrong. But any guidance you can provide is appreciated :cool: