In the case of Oglesby Grocery Company v. United States in 1920, the Supreme Court ruled on a matter concerning tax law and business deductions. The Oglesby Grocery Company had purchased stock as an investment but later sold it at a loss. They claimed this loss as a deduction on their income tax return, arguing that it was part of their ordinary and necessary expenses incurred during the taxable year. However, the Commissioner of Internal Revenue rejected this claim stating that losses from sales or exchanges of capital assets were not deductible under existing laws. The Supreme Court sided with the government's position, ruling against Oglesby Grocery Company. The court held that such losses could only be deducted if they were directly tied to one's trade or business operations - which wasn't applicable in this scenario since buying and selling stocks was not part of company’s regular line of business activity.

The dissenting opinion in the case of Oglesby Grocery Company v. United States argued that the majority's interpretation of Section 2(a) of the Clayton Act was incorrect and overly broad. The dissent contended that this section should not be interpreted to prohibit all price discriminations, but only those which lessen competition or create a monopoly. They believed that there must be an actual or potential injury to competition for a violation to occur under this act, rather than merely showing different prices charged by sellers without any proof of harm on competition. Furthermore, they disagreed with the majority's view about "meeting competition" defense where it is allowed even if it results in price discrimination as long as it doesn't injure competitors unfairly. In their view, such interpretation could potentially lead to misuse and manipulation by businesses seeking loopholes around anti-trust laws.