Ok, nobody coined this in both discussions, so here is something interesting for you to consider about the power of the opt-out.
There was a rather famous study on organ transplant donations consent rates in psychology.
…you will notice that pairs of similar countries have very different levels of organ donations. For example, take the following pairs of countries: Denmark and Sweden; the Netherlands and Belgium; Austria and Germany…
So, what could explain these differences? It turns out that it is the design of the form at the DMV. In countries where the form is set as “opt-in” (check this box if you want to participate in the organ donation program) people do not check the box and as a consequence they do not become a part of the program. In countries where the form is set as “opt-out” (check this box if you don’t want to participate in the organ donation program) people also do not check the box and are automatically enrolled in the program. In both cases large proportions of people simply adopt the default option.
Considering this, the most efficient way in your case would be to use an opt-out. But is this way the most ethical? The standard practice is to use the opt-in. Honestly, I would feel that I am taking advantage of human behavior mechanisms here, if I would choose to use the opt-out, because it's so powerful. I wouldn't be surprised if it's considered a shady UX pattern. So I would choose the opt-in.