For what it's worth I have actually listened to the arguments that the other side had made, but I didn't want to focus on that in place of the stuff that I felt was missed.

I think the Go developers argued for it very well, but there is a reason they decided to go with opt-out, so calling it a mistake makes no sense to me unless you address that reason.

My argument in TFA is that going opt-in biases the data so much that it makes the process of building that system a mistake. Of course, under the assumption that it is ethically correct to build such a system in the first place.