If enough people would return the milk, the store would get the message.
“The extra few dollars cost of spoiled milk is well worth the tremendous spiritual benefits to ones neshama of exclusively using Cholov Yisroel”
Kosher milk from a kosher animal is kosher. Period. You want to think your neshama is better than someone else’s because a Jew owned the cow? Fine. There is far greater spiritual benefit to not robbing someone of his hard-earned money by selling him spoiled milk.