Did DiZ force Roxas to join the Organization? Of course not, Roxas dfecided to join the Organization of his own free will.
So Roxas was a bad guy, did bad things, oh no, guilt trip, decided to leave. Whoops, now the Organization is after him because he betrayed them. Nice job Roxas
Roxas goes around trying to find Sora, oh no, Riku, *whacked accross the head* now he's unconcious.
DiZ needs him to help Sora regain his memories, so he places Roxas in a virtual world of his old home, with his old friends, allowing him to live in happiness while he assists Sora in regianing his memories. So now he lives off his days in a virtual world, living perfectly happy.
DiZ could have just placed him in a tube and let Sora suck his memories from there, but instead he allows him to live in a utopia. Roxas blew off Axel when he left the Organization, which gives Axel even more of a motivation to save him, so Axel hacks into the virtual world and tries to get Roxas back
DiZ tried to protect Roxas from the painful truth, but Namine was selfish and went to go see him anyway, which just caused more confusion and pain for Roxas. Out of Roxas's own curiosity (Fed by Namine's talk with him), he goes to the Manor, and using the clue that Namine left for him, gianed access to the real world.
Roxas made his way to Sora, but Axel stood in his way. And why was Axel there? Because he cared for Roxas and tried to save Roxas. Now what did Roxas do? He killed Axel. Yep, Axel stood in the way of Roxas, so Roxas killed him.
So Roxas finally reached his goal, he found Sora. DiZ was going to allow Roxas to live off his final days in his utopia, surrounded by his old friends, and then quietly have him merge with Sora, but now that Namine made Roxas aware, Roxas grew curious and ventured into the real world
DiZ had no choice, Roas already knew he was in a fake world, so he explained to Roxas what he had to do. He revealed the truth to Roxas, that he was apart of Sora, and that in order for Sora to awake and protect the world, Roxas would need to sacrifice himself. DiZ left the option up to Roxas, and Roxas did the right thing by merging with Sora
So everything that happened to Roxas was a result of his own actions, and Namine's. Roxas joined the Organization, was evil, left causing them to seek revenge on him, blew off his old friend which resulted in his friend trying to save him, was captured and placed in a virtual world of his own, where his old friend who he blew off came to save him, Namine revealed the truth to Roxas which resulted in great pain and confusion for him, and resulted in his curiosity leading him into the real world, where he killed his best friend for standing in his way, then found his True Self, Sora, and had DiZ explain to him why he was needed, in which Roxas sacrificed himself to awake Sora
And on top of this, Roxas also caused the Organization to seek out Sora and Kairi, and eventually having a spaz attack and tried to kill Sora inside his own head