One point about the demands on Serbia -
They were intended to be refused, because ongoing issues with Serbian terrorists had made it pretty obvious that the Serbian government had either no ability or no interest (or both) in addressing the problem, and there was supposedly evidence of high level support for it. The idea was to invade and clean out the nest of vipers, whether the Serbian government wanted it or not. In the process, occupying Serbia and setting up a more amenable puppet government would probably have been the result, not an outright conquest of land. It was certainly "aggression", but in the form of an overly harsh response to a very real threat and a lackluster initial reply by Serbia.
If I recall correctly, the plan was in fact to place a puppet government over Serbia. The Hungarian court in particular was adamantly opposed to adding even more Slavic land to the Empire.
In other words, when someone breaks into your house with a gun to rob it, and you shoot them and steal their shoes, two wrongs do not make a right, but you can't blame it solely on the home owner who was protecting his house. The severity of the response may not have been completely appropriate, but would probably have been considered legally "justified", except for stealing the robber's shoes afterwards. Austria was clearly working that shady area between victim and aggressor.
I don't completely disagree, the murder of the heir to the throne of a hereditary monarchy is about as "act-of-war" as it's possible to be, but let's point out a couple facts.
First of all, this homeowner proposed to actually chase down the robber after the house was robbed, kill him, and steal his shoes. Make no mistake, the war Austria wanted on Serbia was an act of reprisal, not self defense
Second of all, this was a terrible idea because the robber has ties to the Russian Mafia, and even if you're buddies with a guy who works out, that's still bad odds.
Germany was staring at the high probability of an eventual war with both France and Russia (at least in part because of French desire to regain A-L), and while their preemptive declaration of war was clearly an illegal move (especially going through neutral Belgium), it was not without a perceived pressing need. Whether that perception was accurate or not is very debatable, but it's pretty obvious that it wasn't done purely for expansionist reasons (although that probably factored into it to some degree). In other words, clearly guilty, but with extenuating circumstances that reduce the degree of guilt.
I don't agree with the idea that naked aggression is extenuated by the fact that it is necessary to permit even more naked aggression. If France and Russia had done anything against Germany in terms of a war of aggression (or in France's case, reconquest) they would have done it with no help from Britain, and they knew it. And they would have been facing a sizeable coalition of medium-sized powers alongside Germany as well (Italy, OE, A-H), not to mention a Germany that itself wasn't even blockaded just a little bit and so was able to use its full strength.
Germany had the alliances in place it needed to keep France and Russia at bay as long as Britain stayed neutral. There was no need for preemptive aggression until Serbia kicked over the house of cards. I'd argue there was no need for preemptive aggression even then. There are ways to deal with a rogue state without turning it and most of the rest of Europe into a rubble pile.
We can thank French and Russian policies for a lot of the extenuating circumstances, although they in turn had their own justifications. There was plenty of blame to share between practically all involved (probably not Belgium), even though Germany almost certainly deserves the largest slice of the stinking brown pie.
I really feel that Austria gets most of the pie. They were the ones that ultimately turned an international crisis into a shooting war.