this deserves a longer answer than I have time right now, but I think I'm not really in first instance thinking about the contrast between the scientist and the politician (ie the parlamentarian, or member of government) but between Me-the-scientist and Me-the-citizen.
As a citizen, I can freely advocate for actions/positions and there is no obligation (legal or otherwise) that in doing so I *have to* engage with other positions
at least, not in any straightforward way that I can see