Why are drugs that target cell wall synthesis useful?

Bacteria have cell walls made of a protein called peptidoglycan that protects the cell from the exterior environment. Without the cell wall, the bacteria will be susceptible to destruction by chemicals outside the plasma membrane (which is just inside the cell wall of bacteria), and it will not be able to survive. Animal cells do not contain cell walls, so these drugs will only harm the bacteria and leave the cells in the body unharmed.