“Tisha B’Av is when we focus on what we are missing — the Bais Hamikdash.”
Some choose to focus on WHY it is missing and use the day to motivate themselves to correct it. You spend the day in a way that is most appropriate and meaningful to you, others will spend the day in a way that is most meaningful and appropriate for them. If you cant fargin them that, perhaps THAT should be what you work on for yourself , Tisha B’av and the rest of the year.