I think what johannes1234321 is concerned about is that while you say the work is intact, he can't actually vouch for that because he didn't do it. You did. Which means that he could potentially be blamed (or praised) for something he didn't do in the event that you don't keep his work intact (intentionally or otherwise).
Ah ok, thanks for the clarification. Yes, that is technically a possibility, but to be fair, a big takeaway from this whole thing is that signed commits are the only way to really have guarantees of authorship. If you're knowledgable enough to do that, you probably have a reasonably clean commit history, which we generally don't squash before merging.
