Hold on, if a feeling can exist independently of thought like that, and if it's a very nice feeling to have, then is it purely a matter of hedonism? What makes a person choose between basking in "oneness" versus basking in "separatedness"? Why do you assume any such oneness even exists? Darker modalities for the human state of awareness do exist on the left-hand path (beyond superficial egocentrism), so I do believe a conscious choice, based on examination of the variables at play and the expression of personal character, is involved.
Surely there is oneness or there isn't, and the fact will remain constant regardless of what you 'feel' about it. Being one is much different than feeling one (and the latter could obviously result from the former). Of course you can never be a whole constituting a variety of parts beyond yourself, since you are by definition limited to yourself, which is why you often repeat that oneness involves loss of self. And yet simultaneously oneness involves not a surrender to pure feeling but quite the opposite a mechanical transformation of the self into a supposedly 'non-self'.
It seems to me the 'experience of oneness' is surely a self-contained experience of specific conventional stimuli, that may well be described as maintaining a state of awareness in a healthy way in full realization and acceptance of the real nature of the human condition and reality at large, but that should not be described as magically grasping reality at large precisely despite the human condition by transcending it as if it's a piece of litter to be tossed aside.
If you deny the human condition then your experience is a generic blob of undifferentiated oneness akin to the womb, without color, expression or individuality. I have long reviled this false path of weakness for the deception promoted by its supporters in the marketplace of ideas. It represents the most far-fetched, blindest faith as it declares that if it feels good then it must be good, that it is ineffable and therefore cannot be disputed and that it is boundless (without markers or points of reference, hence the ineffability) and therefore of a higher order. It's like being a drug addict and having no idea whatsoever that you're taking drugs or that it might be bad for you. It's the most comfortable escape possible, the most comforting lie.