Data collection becomes an anti trust issue because as you mentioned, you cant really opt out of the data collection part while continuing to use the service. Even a small social network is sort of a monopoly if all of your friends and family is on that network. That way, even the competitors wont solve the data collection part. I am assuming unless the rules are in place, every one would just keep collecting maximum data.

Adversarial interoperability also means there is incentive for both the incumbent and competitor to keep innovating to keep the audience there (and be mindful of newer ones emerging) and hence the best for the customer.