What was the moral when Darry fought his ex-best friend Paul Holden in The Outsiders?

I think the moral is quite clearly stated by Ponyboy in
Chapter Nine of this excellent novel, which narrates the rumble and how Darry and Paul
Holden begin to engage each other in a fight. We are given their history and how Paul
Holden and Darry used to be best friends, but now, Ponyboy points out how ridiculous it
is that they are enemies just because of circumstance. Note what Ponyboy tells us as
they begin to circle each other:

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Even I could feel their hatred. They used to be
buddies, I thought, they used to be friends, and now they hate each otehr because one
has to work for a living and the other comes from the West Side. They shouldn't hate
each... I don't hate the Socs any more... they shouldn't
hate...

It is clear therefore
that Paul and Darry are an example of the completely unreasonable hatred that exists
between the two groups in this novel that only exists because of circumstance rather
than for any other more meaningful reason. Clearly, Paul and Darry in an ideal world
still should be best friends, but the poverty of Darry and what happened to his parents
has taken him out of the world of the Socs and now they stand, irrationally, on opposing
lines, fighting each other.