It seems pretty simple to me. If you don't know what pronoun to use then the correct one is "they", and if you do know then using the wrong one or deliberately

It seems pretty simple to me. If you don't know what pronoun to use then the correct one is "they", and if you do know then using the wrong one or deliberately going out of your way to avoid one is just rude. Obviously, lots of answers will flow perfectly naturally without using pronouns and those should be fine like that.