Putting on my lore hat makes it even more on the nose. The royal family of Alderaan were sympathetic to the rebels, but that hardly represents the whole of the planet of civilians. Its about as valid as Isntreal's choice of bombing whole city blocks because they thought everybody was Hamas. The scene in question isn't even about Alderaan or rebels at all; it was a threat during Leia's interrogation.

You would prefer another target? A military target? Then name the system!

and after she reveals Dantooine as the base...

You're far too trusting. Dantooine is too remote to make an effective demonstration, but don't worry. We will deal with your rebel friends soon enough.

It was never about fighting the Rebels/Hamas, its all about terrorizing others into submission.