The short response
Using human shields is prohibited and must be condemned. It does not make those civilians lawful targets or remove the attacker’s duties of distinction, proportionality and precaution.
The evidence
The ICRC states that civilians used as human shields remain protected. An attacker must still take feasible precautions and account for civilian harm in its proportionality assessment. An allegation of shielding also needs evidence about the particular situation.
Why the argument does not follow
This treats wrongdoing by a defending force as permission for an attacking force to disregard civilians. Both forces retain obligations.