Should Science Education be only Factual?

Answering your question i would say that it should primarily be FACTUAL no matter what the date is. Of course gravity should be included after reading your link. If anything, theories should be analyzed, emphasized that they're merely theories, and understood how theories are formed so the students can begin to think about it. The studies of Science and especially Astronomy have mostly been a large collection of speculations that have been built upon and/or proven through out history.