Although the Kami as the Nameless Namekian wanted to inspire hope in humanity due to the evil he experienced on earth, the same evil he experienced influenced him in wanting godhood for its power. Naturally, Kami would believe a god is all powerful like other humans do. But what was his true motivation to become Kami? Was it his desire to improve humanity or his desire for the power of Kami, or both? Not even Kami knows the answer to that hence why he's a complex character. The true genius stems from his impurities, because he believed that becoming god would make him all powerful, but in the end he was lonely like in Yunzabit Heights.
The greed and lust for power he felt led to him carrying a burden he can never truly erase - King Piccolo. The personification of the evil he experienced who wanted to cause as much chaos and destruction as possible before himself and The Nameless Namekian who is now Kami dies. He despises Kami for letting him exist and wanted to ensure Kami regrets his decision to become guardian for the rest of his life. And because Kami cannot kill King Piccolo or himself, he always felt the full guilt of allowing King Piccolo to exist, and questioned his position of Kami until Master Roshi convinced him that his pure motives to become Kami triumphed the evil, that earth is now a safer place because of Goku meeting his friends which was a result of the Dragon Balls Kami created.
Kami and Piccolo represent the good and bad side of the Nameless Namekian, but they also represented that through their individual characters. For Piccolo, his evil desire to kill Goku left him unfulfilled, especially since he knew Goku would return after training in heaven and he would have to train his son afterwards which led to him questioning his fate. However, Piccolo finding his first friend in Gohan made his realize that being evil isn't a must, even if he was born for it and no longer damned his fate. However, a side of him still missed the enjoyment his felt from being evil, since he's the personification of it. This was evident when Piccolo told Gohan that he refused to live with his fellow people because he'd be bored with living peacefully. Although Piccolo fights to protect the earth and grew more good which peaked with his fateful unification of Kami, part of him still revels in the sight of evil because it's literally what Piccolo embodies.
The big difference between Kami and Piccolo no longer questioning their fates was that their reasons were a reflection of the moral spectrum in which they were born from. The Dragon Balls were a reflected of Kami's good side (His desire to improve/inspire humanity) whereas Gohan was a reflection of Piccolo's evil side (His desire to kill Goku and control the world).
This is why Kami and Piccolo can never stand the sight of each other, because Kami and Piccolo are indeed polar opposites by nature. However, when they reunited, the newly good hearted Piccolo was able to become one with Kami, eliminating whatever evil remained in Piccolo's heart and completed the full cycle of The Nameless Namekian's quest to become pure, but in the end couldn't achieve the position he craved. It's beautifully tragic.

I had to re-type this entire post again which was a bummer, I'll most likely add to the post if I've forgotten anything.

