Castles made of sand all die. So do castles made of rock; they just take longer to go.
The point of making a castle is not that your castle will live forever, but that, before it dies, it will be helpful (even if only by being beautiful and making people smile). If you are fortunate, it will inspire, and a trace of it will live on in the future castles built by those who saw yours.
Those who take joy in destroying the castles of other people before that destruction was naturally due not only decrease the diversity of beauty in the world; they also seek to extinguish the hope, the belief that it is worth investing for the future in hope of maybe passing something on, of inspiring.
Those who build castles, even castles that get knocked down immediately, are not fools for wasting resources by taking the risk or even near certainty that their effort will go unrewarded. Because even just the decision to try again, to risk an act of creation, is a blow struck in the fight to keep hope alive.
This metaphor is my castle. If you like it, pass it on.