The main problem主语
is谓语
its prevalence宾语,and the social costs宾语(平行结构）
that ensue from the use by everyone of something定语从句修饰costs
that would be fairly harmless定语从句修饰something
say插入语补充下接的状语从句
if only the rich were to use it状语从句说明上接定语从句的条件
整句话意思：主要的问题在于轿车的盛行和每人的公共消费,但如果只有富人消费,那这笔费用便无关痛痒.
有问题可以继续问我!of something在这里充当什么成分？谢谢！