Not quite clear what specific issue you are getting at here. It might come to me with more reflection, but I'll give my best answer for now.

I am not arguing that my current values are necessarily selfish. They might not even be for the purpose of "thriving". They are what they are regardless of how these values came to be. These values may be sacred to me and I would lay down my life for them. Yes, a researcher might identify a causal pathway that included the search for meaning or the pressure of my parental context. I might even be aware and accept the findings of the research. However, regardless of cause, the sacred remains sacred and may take precedence over any thriving.

So what would be the agenda of my prescriptive research?

1. To identify the structure of the values I do have. For example, to highlight the fact that there is usually a multiplicity of values that could easily conflict in practice. Or to highlight that consistency and universalism are some of my goals.
2. To figure out ways multiple people, each with their own and differing goals can work together.

For both these goals the prescriptive and descriptive researchers must collaborate. Or, at least, the descriptive researcher has much to teach the prescriptive practitioner.