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.