Germany was not
the aggressor, although I will concede that it was
an aggressor, but that label is effectively meaningless since everybody was that to some degree.
Serbia, or at the very least, elements of the Serbian government, had been sponsoring terrorist acts in Austria-Hungary for several years as of 1914, while at the same time doing ethnic cleansing of its own in the territories taken from the Ottomans after the First Balkan War. Serbia could've completely derailed the train to WW1 by simply not being a dick.
Austria-Hungary had a right to defend itself, a right it had been repeatedly denied as Russia would back Serbia due to Pan-Slavism. It is not surprisingly it overreacted, unfortunate but understandable.
Russia was the state that decided to take a stupid Balkan scrap and escalated it into a potential continental war. This it did with the encouragement of France.
France, Germany, and the UK vastly overestimated the military and economic growth of Russia during this period. That is why Germany figured a war now would be better than a war later where they would get smashed between a revanchist France and a juggernaut Russia.
'In March 1913, massive sums were approved by the Tsar for artillery and other armaments in a vastly ambitious scheme that would by 1917 have increased Russian winter peacetime strength by 800,000 men, most of whom would (in contrast to the deployment plan of 1910) be concentrated in European Russia. As a consequence, the peacetime strength of the Russian army in 1914 was double that of the German, at around one and a half million men and 300,000 more than the combined strengths of the German and Austro-Hungarian armies; by 1916-1917 the Russian figure was expected to exceed 2 million.' (The Sleepwalkers, page 331)
This is also why France encouraged the war. If Russia grew too powerful, it wouldn't need the alliance with France anymore and would be able to forge its own path.
'That French policy-makers were willing to accept the resulting constraints is demonstrated by their willingness to extend the terms of the Franco-Russian alliance specifically in order to cover the Balkan inception scenario, a concession that in effect placed the initiative in Russia hands. The French were willing to accept this risk, because their primary concern was not that Russia would act precipitately, but rather that she would not act at all, would grow so preponderant as to lose interest in the security value of the alliance, or would focus her energies on defeating Austria rather than the 'principal adversary', Germany.
'The Balkan inception scenario was attractive precisely because it seemed the most likely way of securing full Russian support for joint operations," (The Sleepwalkers, page 351)
As for Great Britain, I am quite certain that the dead of the Bengal famines far outnumber those of the Herero. This is also the Great Britain whose acting under-secretary of the Foreign Office Sir Francis Bertie told the acting German ambassador in 1897 that "should the Germans lay so much as a finger on the Transvaal, Bertie declared, the British government would not stop at any step, 'even the ultimate' (an unmistakable reference to war), to 'repel any German intervention'. 'Should it come to a war with Germany,' he went on, 'the entire English nation would be behind it, and a blockade of Hamburg and Bremen and the annihilation of German commerce on the high seas would be child's play for the English fleet.'" (The Sleepwalkers, page 149)
And people wonder why Imperial Germany built a navy.
And I'm not getting into the very illegal nature of the British blockade in WW1.
I think you're overstating the level of acceptance. Asquith wrote at the time that Austria had bungled matters by taking a situation in which they had the better argument on most of the points and turning it into one in which it appeared a major power was bullying a minor one.
There was a commonly accepted way to properly do this sort of thing, as evidenced with the Treaty of Berlin in 1878 or Agadir, which basically came down to a three point process.
1. Dispute arises between major power and minor power(s) which cannot be immediately resolved.
2. Great Powers meet at a conference to decide what must be done. Much diplomatic ink will be shed and notions of spheres of influence debated until it's decided what is appropriate for either power to concede. The major power will often be represented directly, or by a close ally, the minor power by an advocate for the case.
3. A decision acceptable enough to all major powers involved in the relevant alliances is reached and passed on down to the minor power to be accepted.
Europe would have accepted a small conference in which it was decided Serbia should comply with the vast majority of the points- everything short of abject humiliation. What many of the public in the Entente nations would not accept was a unilateral imposition of such by a major power on a minor one.
Look at this from Vienna's point of view. Who would be the major parties in a conference? Austria-Hungary, Germany, Russia, France, Great Britain, and maybe Italy.
Russia-will do its utmost to protect Serbia from suffering anything at all
France-will back whatever Russia decides, see above
Italy-will do whatever it can to stick it to Austria-Hungary
Germany-they'll back us
Great Britain-will someone please explain why their opinion should even matter here? And even so, they've been buddying up to France and Russia