Back in elementary school (I believe it was second grade), I remember being taught never to start a sentence with the word “and” or “because.” My teacher even created two “clubs,” the And Club and the Because Club, for students who dared to use those words incorrectly.* The message was simple: You don't want to be in either club.
*We were also cautioned not to start a sentence with the word “but,” but there was no But Club. I leave it to the reader to ponder the reasons for this omission.
Now that I work with high school students on a pretty frequent basis, I'm learning that I was far from unique in being taught these things many years ago. In the past year, I've probably had a dozen different people assert that it's not okay to start a sentence with the word “because.” Years after learning how to write much more interesting sentences, they're still trying to stay out of the club.