I completely agree with the idea that Sora's attitude is an important plot point, although I never thought it to be a way for Sora to cope with different situations, that's a cool concept.
However I don't think Roxas is a character that reacts angrily ALL the time. As we can see in KH2, Roxas is a well adjusted, even-minded and practical individual, as he apparently serves as the glue guy in his group of friends (Hayden, Pence, Olette). However his life was unceremoniously interrupted with by the Org. and Diz (and the fact that he doesn't really exist). Therefore I think we can cut the guy some slack if he wanted to release a little steam.
Also we can see even before his fabricated reality in KH2, Roxas was a pretty chill dude. In 358/2 Days (after going though his initial zombie phase) he's exhibits an innate kindness towards various Organization members and especially Axel and Xion.
And let's not forget the fact that he willingly goes back to Sora, accepting his fate and helping him throughout his journey.
So yeah, I like Roxas haha