Late reply, apologies. And let me first thank you for the provided context.
My notion is, that anything labeled as solidarity has to be an act of free choice. Using Solidarity for a forced "choice" is an example of doublespeak. For context, another example for doublespeak is the "USA Freedom Act" policy that brought mass surveillance.
To answer your question for a word I'd prefer: How about an ontologically expressive word like "collectivity principle" / "Kollektivitätsprinzip". Coincidentally, I just googled it, "Kollektivitätsprinzip" is used in Switzerland instead of the word "Solidaritätsprinzip". Becks the question why Switzerland is honest where Germany uses doublespeak?
To finish, you can see that I am not arguing against the "Solidaritätsprinzip", no, I argue against the dishonesty of using doublespeak. A futile undertaking, but sometimes I cannot help myself.