@TheD:
Raising the bounties of pirates that saved a country is equivalent to listing the killing of the mafia boss as a crime committed by the serial killer. Ofc it doesn't excuse the serial killer from his previous crimes, but it should at least be acknowledged that he's killing other bad guys and shouldn't be listed as another crime.
On the contrary, the fact that he killed a mafia boss tells that he is much more dangerous than previously thought. He's not only an ordinary serial killer, but also a serial killer that took down a goddamn organized crime boss. His threat level rises (which is the metric used for bounties).
It might not be considered a crime, but the killer will get way more priority from the police, especially to save face as the killer managed to do what the police couldn't.
@TheD:
The case with the Yonkos inhabiting islands is different from Luffy saving Dressrosa. It can be assumed by the general public that the Yonkos only do this for their own benefit since they rule over the islands. It's different with Luffy and Law though. They saved Dressrosa, but didn't take over it. King Riku still remains the king. They didn't gain anything from it.
Neither did Whitebeard, as Neptune was still the king of Fishman Island.
The general public can perfectly and reasonaby assume that Luffy had no kind intentions in saving Dressrosa. In fact, it could very well be said that he only saved Dressrosa because he wanted to defeat Doula Mongo in order to survive, and Dressrosa was released as an inevitable consequence. No one knows that Luffy did all this because of the friends he made in Dressrosa.
@TheD:
And yes, Akainu did order Fujitora to capture Luffy and Law or he would be banned from all the marine bases. But Fujitora pretty much responded with "sure, ban me from marine bases, im not capturing them".
Which shows exactly why Luffy and Law will get their bounties raised. The Marines do not want to admit that the Straw Hats saved Dressrosa, so they want to save face by catching the people who defeated Doula.
It would be insane to not increase their bounties, as they're wanted even more by Akainu after this incident.
Essentially, it doesn't matter if they're heroes or not according to Fuji. They're still criminals, and the WG has an even bigger reason to increase their prices. Remember, Luffy still has a bounty of 400 Million and Law a bounty of 440 Million, so worrying about public image for raising those is, well, dumb, because those bounties are already very high anyway.
If public image is a concern, why not just drop the bounties altogether then?