A lot of this sort of A/B testing has the character of a psychology experiment. If it were conducted by a reputable research lab, it would have to pass an instituational review board who would weigh in on whether it was an ethical experiment, and among other things research subjects would always have the right to decline to participate in the experiment.

But when private companies do it, nobody holds them to the same standard of ethics in their human experimentation. But clearly people’s right not to be subject to psychological experiments without their consent is being violated.