I have been thinking about this question. And sure, you can take Sengoku's word literally and believe him wholeheartedly about Rocks.
But let's all take a second and remember some facts:
1- Sengoku is a Marine, he will NOT say "they are good pirates".
2- Sengoku himself admitted that Rocks was looking into "Taboo Subjects". We all know that means void century, once piece...etc (something Roger ended up doing)
3- WG tried to cover everything about Rocks, even the island itself was erased from history books and from the maps
4- Garp having a bad taste about the incident of "God Valley" and it being involved protecting celestial dragons and their slaves.
5- The fact that we know how good-natured Old Man Whitebeard is, and the man STILL followed him. I may even consider him more good natured than Roger for the simple incident of Squard and his crew getting annihilated by Roger pirates.
The point is, Whenever the WG talks about someone who is a big threat to them, they picture them as demons, worst criminals...etc and all kinds of stuff. They literally brand them with the worst of descriptions. Sengoku even did that with Luffy when Luffy was about to free Ace from execution platform. Sengoku was like "you too are a sinful pirate who needs to be executed" and so on.
I honestly think that Sengoku and the WG are not telling the whole truth here. When the Sengoku says that Xebec wanted to be the king of the world. Most people acted like he was a tyrant. BUT what if he simply knew of the exitance of Imu-sama? What if he simply wanted to liberate the world from Imu-sama and celestial dragons. Something just like what Dragon is trying to do now.
BUT because Xebec was defeated, and because the WG now can control its history books and what they teach. they altered some facts and ended up changing the idea of "liberating the world from Imu-sama and Celestial Dragons" into "he was a tyrant who wanted to be King of the world"
I TRUUUULLY think that Roger during that time, he still DID NOT KNOW the truth about those subjects. I think Xebec was seeing the full picture and he was waging his war on the WG for it. While, luckily for Garp, he met Roger who simply had Xebec as a fellow pirate rival. And after stopping and taking down Xebec. Roger followed the SAME PATH Xebec went for after he learnt the full truth when he became pirate king.
I think it's clear that Sengoku was implying about Garp hated that incident because he protected the celestial dragons. I think there is more to this detail than just Rocks was attacking celestial dragons and Garp protecting them.
The fact that the WG after that incident ERASED the island, it means they were hiding some atrocities they were doing, or some important info! Otherwise, the island would have stayed! And would have marked and celebrated as an island where navy beat the Rocks. BUT the island had too many secrets, BAD for the WG, and I think both of Garp and Roger after their defeat to Xebec, it left a terrible taste in their mouth. Their victory was bittersweet.
That's just my opinion
I think that people are jumping to conclusion about Xebec being evil. I think he was the guy who after his defeat, he was the guiding light for Roger to know the full truth. And Roger ended up becoming pirate king and then now, he's beyond Evil for the WG as we can all see.
But let's all take a second and remember some facts:
1- Sengoku is a Marine, he will NOT say "they are good pirates".
2- Sengoku himself admitted that Rocks was looking into "Taboo Subjects". We all know that means void century, once piece...etc (something Roger ended up doing)
3- WG tried to cover everything about Rocks, even the island itself was erased from history books and from the maps
4- Garp having a bad taste about the incident of "God Valley" and it being involved protecting celestial dragons and their slaves.
5- The fact that we know how good-natured Old Man Whitebeard is, and the man STILL followed him. I may even consider him more good natured than Roger for the simple incident of Squard and his crew getting annihilated by Roger pirates.
The point is, Whenever the WG talks about someone who is a big threat to them, they picture them as demons, worst criminals...etc and all kinds of stuff. They literally brand them with the worst of descriptions. Sengoku even did that with Luffy when Luffy was about to free Ace from execution platform. Sengoku was like "you too are a sinful pirate who needs to be executed" and so on.
I honestly think that Sengoku and the WG are not telling the whole truth here. When the Sengoku says that Xebec wanted to be the king of the world. Most people acted like he was a tyrant. BUT what if he simply knew of the exitance of Imu-sama? What if he simply wanted to liberate the world from Imu-sama and celestial dragons. Something just like what Dragon is trying to do now.
BUT because Xebec was defeated, and because the WG now can control its history books and what they teach. they altered some facts and ended up changing the idea of "liberating the world from Imu-sama and Celestial Dragons" into "he was a tyrant who wanted to be King of the world"
I TRUUUULLY think that Roger during that time, he still DID NOT KNOW the truth about those subjects. I think Xebec was seeing the full picture and he was waging his war on the WG for it. While, luckily for Garp, he met Roger who simply had Xebec as a fellow pirate rival. And after stopping and taking down Xebec. Roger followed the SAME PATH Xebec went for after he learnt the full truth when he became pirate king.
I think it's clear that Sengoku was implying about Garp hated that incident because he protected the celestial dragons. I think there is more to this detail than just Rocks was attacking celestial dragons and Garp protecting them.
The fact that the WG after that incident ERASED the island, it means they were hiding some atrocities they were doing, or some important info! Otherwise, the island would have stayed! And would have marked and celebrated as an island where navy beat the Rocks. BUT the island had too many secrets, BAD for the WG, and I think both of Garp and Roger after their defeat to Xebec, it left a terrible taste in their mouth. Their victory was bittersweet.
That's just my opinion
I think that people are jumping to conclusion about Xebec being evil. I think he was the guy who after his defeat, he was the guiding light for Roger to know the full truth. And Roger ended up becoming pirate king and then now, he's beyond Evil for the WG as we can all see.