The allies were the bad guys
This was a war crime. The Geneva conventions only allowed bombardment of a city that was defended by the enemy on approach to the city: that is, the opposing side had to decide to use the town as a fortification.
1) There was no large enemy presence to use the city as defensive stronghold. The wanton destruction of the enemy infrastructure and the murder of enemy civilians was out and out murder and a capital war crime
2) The allies were not "on approach".
3) it was done to murder civilians, an 25,000 are (((LOW estimates)))