The Gemara cites the opinion of Rabbi Chanina Segan HaKohanim who maintains that it is worth it for the destruction of the Bais HaMikdash that even one who requires immersion not immerse in a hot mikveh on Tisha B’Av.
Regarding one who is weak and has difficulty fasting on Tisha B’Av, the Mishna Berura (Orach Chaim 554:51) writes that nonetheless, it is worth it for one to be distressed over the Bais Hamikdash at least once a year. Indeed, the Shulchan Aruch (Ibid 1:3) writes that a G-d fearing person should be distressed and worried over the destruction of the Bais HaMikdash. While it is difficult in our contemporary society to fathom the importance of the Bais HaMikdash, we can rely on the Shulchan Aruch as we do regarding all Halacha and take the time to think about our loss throughout the year.
The Gemara (30b) states that one who mourns Yerushalayim will merit seeing its joy and one who does not mourn Yerushalayim will not merit seeing its joy. Merely the knowledge that we will soon merit the joy of Yerushalayim and the Bais HaMikdash rebuilt should inspire us to mourn the destruction of the Bais HaMikdash properly, and then HaShem will console us with the greatest joy, with the arrival of Moshiach Tzidkenu, speedily, in our days.