When Waltfeld attacks Tassil he does destroy their food supplies and stockpiles of weapons but he doesn’t kill anyone. (There are a few who get injured though.)
In response the young Desert Dawn people go after Waltfeld’s force. Not wise. Most of them die then Kira catches up to the survivors and defeats Waltfeld’s troops. But then he gets out of the Strike and gives Cagalli a piece of his mind about how stupid she was to go after the ZAFT group. He also smacks her.
Honestly they were pretty stupid. The situation was pretty bad though. They felt powerless in the face of their families not having food and shelter. I do feel like they should have focused on their feelings of relief at their family members being alive. But I can understand why they were upset and decided to go after Waltfeld.