@Razh:
I'm just saying they could have avoided the war if they wanted it. There are ways. At the very least, they didn't have to make a worldwide show out of the execution. They could have kept him locked up in ID or strangled him in his cell. They wanted both to make and example and to draw WB out to his death.
There were unreliable Shichibukai, who still contributed more to Marines' side (all in all), but there was also stuff like: hatching a plot to turn WB's allies against him, summoning most of Marines' might to Marineford, Wapometal walls, shitload of Pacifistas.
From what I took, it was a calculated risk. They didn't need to defeat WB's entire force. They just needed him and Ace to die.
The thing about Marineford though is that it was meant to be a show of power. The Marines weren't trying to really act proficient in just finding any way possible to have Ace and Whitebeard die in and of itself. They wanted to take advantage of Ace being Roger's son as a way to provide a deterrent for the great pirate era. If Whitebeard either refused to come or lost the battle (especially without saving Ace), that inhibits the morale of piracy a lot by showing Whitebeard's weakness emotionally, mentally, physically, or a mix of all three elements. But it ended up backfiring on them the moment that Teach showed up, leading to Whitebeard confirming One Piece's existence and inciting a whole new age of piracy rather than how the Marines wanted to hinder the allure of law-disregarding freedom.
It wasn't that they really NEEDED to make a whole grandstanding out of Ace's execution, but because they wanted to. Marineford wasn't really a war of conviction as much as it was about pride and egos. And it sort of makes sense with how a big a role selfish dreams and inspiring others play in the series. So really, it's just fancy Oda being fancy Oda. They weren't trying to keep the balance, this is the one opportunity they saw where they could gradually turn the balance over to their favor. The Gorosei always likes to stress the importance of the world balance, but that doesn't equate to not wanting the World Government to be the top dogs if they have the opportunities to do so. They're just really methodical and reactionary about it rather than kickstarting any major plays themselves. But with Akainu being the Fleet Admiral nowadays, that might change.
Ace could have stayed in prison, but that would end up leading to the World Government needing to make a decision to start a war regardless. Because if Whitebeard raided the place and got Ace out while the World Government just stands by and does absolutely nothing about it, then they in turn end up looking weak and indirectly giving more credibility to the capabilities of piracy. As long as they were keeping Ace in general, a war was inevitable. So at the end of the day, it was just a simple decision about wanting to let the world stay exactly the same as it is with a slight risk of the World Government losing morale if word got out of them letting Ace go, or taking advantage of this rare opportunity.
But this is Age of Pirates, and there's more of them than ever before. Your description of Emperors is funny and partly true, but we've seen how serious everyone on WG side became just from hearing 2 of Emperors are about to meet.
And even of you remove 4 of them out of the equation, there are plenty of other power hungry pirates who might become a great risk over time. I doubt WG survived 800 years by just reacting to various events in the world. WG is all about control. They were even controlling the lack of control they had over the world, ffs. All the while they've been developing weapons. I just wonder if they will be the first to make their move, or will someone force their hand to act. Luffy, Dragon or Blackbeard, for example.
Well, all we hear about the Blackbeard Pirates is how they're amassing a bunch of Devil Fruit powers and weapons all of the time. Kaido's trying to build up a Zoan army. And Big Mom at least has Pudding and wants Germa's tech for something that's probably related to giants. So it's not like everybody besides the World Government is necessarily slacking off. I think the Reverie will give us a decent impression as to who might be willing to make the first big play.