Rebasing is not the problem, squashing is[1]. I never understood that. To me, it suggests the person does not understand branch merges. You should either:

A. Rebase on top of master, keeping all commits; or

B. Merge the branch, keeping branch history.

[1] Obviously squashing has good uses, too, within the branch. Maybe you want to squash together all commits for a particular feature's implementation (while still keeping the specs for same in a separate commit, hopefully).