Making things "opt-out", without even making it hard, dramatically increases the number of people who opt-in. It can be used for many reasons.
For example, the UK switched it’s organ donation laws from opt-in to opt-out.
Another example, my government has decided that them selling their citizen's personal information to garages, insurance companies, etc, when we buy cars, should also be opt-out.
So they freely sell the car make, acquisition date, buyer's name,… [1][2]
Unless it has changed with GDPR. I’ve never bought a car.
While we're on the topic of GDPR, that is exactly why it insists on making cookies, tracking, and the "sharing of information with partners" opt-in.
And that is without hiding what you’re doing, making it unclear or confusing, or requiring multiple actions to change it.
(Links in French, sorry)
[1]: https://mobile.interieur.gouv.fr/Repertoire-des-informations...
[2]: https://www.carte-grise.org/actus/2014/05-12-L-Etat-vends-le...