Is it OK to use the word "queer?"
Well, it's tricky. Only since the beginning of the 20th century has queer been used to refer to people who identify as gay or lesbian. And for much of that time, it was used in a derogatory manner.
More recently, queer has been reclaimed by the LGBTQ community (hence, the Q) and functions as both an umbrella term and as a specific identity. But, for some, queer may still conjure feelings of being different, ostracized, or not accepted. Since the term is not universally accepted, some people recommend avoiding it unless quoting someone or describing someone who self-identifies that way.