It's not unreasonable to force push a branch. Anytime you've rebased but already pushed you would need to do so. I've worked on an open source project where every commit was required to pass all the tests, so if you submitted a PR that had any commit fail CI, you would have to alter history and force push.

I also just like pushing to a branch on Github, even if I might rebase later. Circle CI is triggered through Github, so it's nice to have that triggered for me. Our staging servers (production data, your branch's code) are deployed from Github branches as well. Plus looking at diffs on Github is really helpful for me to spot errors—I'm not sure if it's the context switch away from my text editor, Github's diff UI, or what, but it works for me.