Wasn't it? But I suppose it was thought that it would save more lives in the end. There were a lot of lives lost - it is not easy to know what would have been the best course of action from this time distance.
This was a few weeks after Dunkirk, and British troops were still being evacuated from Normandy and Brittany. On 17 June 4000 people were on the Lancastria when it was bombed off St Nazaire, laden with troops and refugees who had been taken aboard to be transported to Britain. The same day, German aircraft bombed a rail junction at Rennes where twelve trains were waiting, some full of retreating soldiers, some with refugees, and one full of munitions! which exploded, killing at least 800 - that was the number which could be distinguished and buried. Many more were believed killed.
That was just on one day, as Germany was defeating France.