In view of the common hope (I hope) for peace in Northen Ireland, why do Orangemen wish to march commemorating a victory through the villages of those defeated?

Imagine a parade of Yankees marching through Atlanta to celebrate it's burning. If one wants to heal a wound, then one should not rub salt into it it seems to me.

I would like to understand if anyone can help me.

Regards and hope for peace, Fortunato