The singular version of they emerged about 100 years after the word was first termed. While some editors had strong opinions about the singular they from the 14th to 18th centuries, some very notable authors during this time such as Shakespeare disagreed (as evidenced by his use of the singular they throughout his works). It was rarely contested as grammatically correct until society became more aware of people who were using it to define their gender identity and transgender individuals found themselves in the public spotlight with their rights being contested. Unsurprisingly the only people contesting whether it is grammatically proper today are the very same people who do not believe that transgender people deserve the same rights.