My high school English teacher taught us to never start a sentence with conjunctions, but throughout the years I have seen a lot of such usage in academic writings and novels. I have also read various articles, saying that such usage is now acceptable. Is it merely a preference of style or is it grammatically wrong? Does it otherwise imply different semantics from the usage that follows a comma(,)?
For example, are the following sentences acceptable in terms of grammar/formality?
"The organization should have taken the blame. Or, its leader can sacrifice himself for the well-being of all."
"She is one of a kind – she displays high empathy on each and every strangers she meets. But, she lives in a fiction."
"The city is wondrous, in spite of its proximity to my hometown. And, a highly regarded culture resides there."
Thanks in advance.