About the difference between men owning a car and men owning a horse, Holden says,
"Take most people, they're crazy about cars. They worry if they get a little scratch on them, and they're always talking about how many miles they get to a gallon, and if they get a brand-new car already they start thinking about trading it in for one that's even newer. I don't even like old cars. I mean they don't even interest me. I'd rather have a goddam horse. A horse is at least human, for God's sake".
Holden is single-mindedly against the values set forth by the capitalistic world in which he lives. Earlier, he railed against his brother D.B., who he believes has prostituted his artistic talent in order to be successful in Hollywood. He is terrified at the thought of having to grow up and enter the rat-race, of having to toil day after day in a soulless job in quest of the almighty dollar. Cars exemplify for Holden the materialistic values of his society, values towards which he is being groomed to pursue in the series of prep schools he has attended. Holden thinks that this capitalistic way of life is "phony", and despises everything having to do with it.
The idea of owning a horse instead of a car represents for Holden a time when things were more simple and innocent. A horse is at least something that is alive, and to be attached to a horse seems much more satisfying and genuine to him than being attached to material things like cars. Holden longs to remain in a childlike state, where life is simple, and unspoiled by skewed values and the pursuit of lucre at the expense of personal fulfillment. He wants to be "a catcher in the rye", living forever in idyllic simplicity, his only responsiblity the task of guarding the innocence of others like himself (Chapter 17).