Social Networks should be like email providers. You choose one that fits you best, or deploy your own, without having to worry not being able to communicate with others. Maybe we are long overdue for an open standard protocol for social interactions on the web. If you come to think of it, when the personal data itself isn't the property of the company behind the social network, there should be no reason not to share…
This exists as a W3C recommendation (ActivityPub), and before that you had pioneers working on things like StatusNet and GNU Social, way back in 2008.