Or, yeah, angst.
The core services sure but why wouldn't it be like FB in general(full of third party apps and games)?
There's a reason people only integrate with FB to try and take traffic, and even then they become the customer paying for ads. It's not worth your time.
In any case, if making awesome VR a reality was Oculus' vision, they can make a pretty good case for that vision being well served by the resources of Facebook.
At the end of the day, what are people afraid of? That the newest action games won't be playable on Rift? I just don't see how people figure Facebook might ruin this product.
That said, I personally don't know if Facebook is going to mess up Oculus. I imagine that what people are worried about is that Facebook will push for Oculus to be used for social VR and will largely ignore games. VR gaming requires high quality sensory experience in a dynamic environment with fast player movements. Social VR is probably going to be way, way more static, (but will have other demands like monitoring body position, face scanning, etc.)
To make the product valuable, it has to be a good platform which other companies can use.
Facebook has ruined many companies that relied on the facebook api to build their businesses. Sometimes facebook reimplemented someones else idea and then remove features from the api to kill the original company.
Making a product based on the Oculus rift platform is a high risk operation. Facebook has already ruined the trust.
It happens so often many of us just laugh if not smirk the whole time we watch the familiar process play itself out. Eventually they learn they are not the center of the universe.