Rebasing and fast-forward merging are two very different things.

whenever you rebase you create _brand new commits_ based off another part of the project history which bear a strong resemblance to the original commits but are nonetheless different.

adding -i allows you to do further modification of commit contents (reordering, squashing, dropping, etc. but a vanilla rebase is still changing history.

Linus addresses this in his mail early on: "People can (and probably should) rebase their _private_ trees (their own work). That's a _cleanup_. But never other peoples code. That's a "destroy history" "