Chapter 8: Besides money, what does Two-bBt say is the only reason that keeps Darry from being a Soc?

From the text:

"You know, the only thing that keeps Darry from bein' a Soc is us."

"I know" I said. I had known it for a long time. In spite of not having much money, the only reason Darry couldn't be a Soc was us. The gang. Me and Soda. Darry was too smart to be a greaser. I don't know how I knew, I just did. And I was kind of sorry.