The Khedive was a terrible administrator, yes, but that can only explain the Mahdi, not justify his actions. Of course, he thankfully died fairly quickly and was replaced by the Khalifa, who seemed slightly less fanatical. Still, even by local standards he was a heretic; declaring himself the Mahdi was blasphemy. What was bad about blowing up his tomb and throwing the bones in the Nile?

I also disagree about Fashoda. While Cecil Rhodes had an "all red" plan for a railroad from Cairo to the Cape (with a telegraph line along its route), Her Majesty's government never did. The conquest of Egypt ironically happened under Gladstone, who loathed all imperialism, and the government was perfectly content to let the Mahdists control the territory provided that no other power did, because in reality all the British government cared about was that a foreign power not control the sources of the Nile. It was believed that this could be used as leverage over Egypt by building dams to cut off the flow of water or even divert the river's course. Salisbury's government was more worried about the German East African state attempting to push north (indeed, it tried for a time when it got the support of Dr. Emin, the nominal governor of Equatoria).