Unwanted unsubscribe in profile
This is a frustration and I wish there was a better answer. I've asked a similar question myself.
One solution is to use tokens in links sent out in mailings as much as possible, so this checkbox is already selected, but you won't be able to cover all uses with this.
You can use two groups, the first of which is the one on your forms. Then set up a CiviRule that contacts are added to a second group, the real mailing list, when they are added to the first group. But then people who are logged in or using a tokenized link won't be able to remove themselves from the group, so I wouldn't recommend this unless you aren't using tokenized links or allowing logged in users.
I'd like to fix this, at some point.