Why the marines give a fuck about the world government, the gorosei, and the celestial dragons?
But I'm asking because I, and let's face it, WE have the time, and because why do ABSOLUTE JUSTICE aka Akainu would be the Dog ( lol ) of parodied mostly dumb world nobles and 5 shady old guys ?
Why Sengoku would ?
How Garp didn't punch one or twice ( or thrice ) by F***ING mistake ?
Because WG and the marines are a symbiotic relationship.
Let's not forget that 180 countries are governed by the WG, and the WG are the ones that enforce the law that is to be respected by these countries. The duty of the marines is to ensure law and order are to be respected by the persons living in these countries under WG jurisdiction. Marines are also enlisted from these countries to sustain its strength by force and numbers.
Without the marines, the law won't be respected by these countries, said countries will secede, and chaos ensues... but without the WG, the unity between the 180 countries will break down, and the marines will have no law to uphold and hence become redundant. They'll just end up becoming similar to a regular pirate crew with no one to enlist to sustain its numbers. In other words, they'll eventually die out.
And let's say Akainu takes control by killing the WG, replace it with the marines, and manages to take control of the 180 countries. Do you think all the marines under him as fleet admiral share the same grievances? Do you think Kizaru or Greenbull share his attitude to CD's and WG? And what about Issho, do you think he would stand by and see Akainu take complete dictatorial control of the WG under his hands?
Akainu had enough trouble dealing with Aokiji. What about the entirety of the Admirals as well as all the marines? And what about the marines enlisted from these 180 countries? What do you think they will do seeing that the WG is toppled and no law exists anymore to govern and protect their families?
If Akainu goes against the WG, Gorosei, and the CD's, he will achieve nothing but chaos, infighting, and a resulting decline within the marines.
You are talking to me about how the general population might feel.
I am talking to you how about these mighty beings, with each their own philosophy might feel.
Akainu, if perfectionist with his own Absolute Vision of Justice, should 'ot tolerate World Nobles way of living and such, try with his might to rules everybody with what he thinks is right.
The way the marines operate with respect to their preferences of justice is not
what law to uphold, but
how to uphold that law. They are not a legislative branch of the WG; they are the executive branch, who ensure that said law is to be respected by the people, and to the people. E.g.:
-- Aokiji's type of justice is "lazy justice", meaning his justice is more relaxed. He doesn't want the marines to become what they've become in Ohara.
-- Akainu follows "absolute justice", which is the complete opposite... forcing the law and killing those committing acts against the law no matter how small... even killing a kid just because he stole a snickers.
The marines don't write the laws. They execute the laws, but the way they execute said laws are different. If for example, WG puts a law that goes
"it is illegal to save a life", Akainu would kill every doctor there is; and Aokiji would just let them go, maybe to a country without WG jurisdiction (like he did to Robin).
They don't enact laws, they execute it.
Your question around the Celestial Dragon is the same thing. The WG write the laws that say they are to be respected, and any action taken against them is a penalty of death. It is the duty of the marines to enforce that law, not to challenge that law. Garp hated the Celestial Dragons, but even
HE knew that the law had to be upheld, which is why he executed the orders to save them at God Valley.
If Garp went against the order to save the CD's, do you think all the other marines would let that slide? Of course not. Even that random soldier in the room where Sengoku talked about Garp said
"it was the duty of the marines to protect the celestial dragons". Garp would be fighting against 4 admirals, a hundred vice admirals etc to protect his life if he just "punched one or two CD's by mistake" as you put it.