Galileo? Pissed off the Pope, convicted by the Inquisition, spent the last thirty years of his life under house arrest. Don't think you can get much more unpopular than that. Still bloody right, though, wasn't he? If it's a choice between the likes of Galileo, or Martin Luther King, or those heroic women brutalised under the Cat and Mouse Act, or too many more to count, then I'm going with the people who champion heliocentric celestial mechanics, or drag their country out of a barbarically racist collective mindset, or ... You get the picture. Indeed, being unpopular is almost an inevitable consequence of being right about something this important - stupid people will never thank you for pointing their stupidity out to them, after all.
(And if being popular sticks me in with Jolyon Maugham, Nancy Kelley, Aimee Challenor, Adrian Harrop.. I like it over here with the rejects, thank you very much).