Earlier quoted context omitted.
Because of the security and risk implication of not preventing it. Goldman Sachs is both an investment bank and an asset management firm, literally the same company. However, they have clear protocols in place to separate the two sides because otherwise the opportunities for impropriety are too high. I could see a similar argument for separating Facebook and Oculus accounts.
Sure, but Goldman Sachs business model isn't aggregating and selling data. Facebook's is.
In this specific analogy, the point is, despite having different business models, society benefits from either conglomerate separating their respective two aforementioned business units.