Why did plessy argue

Homer Plessy refused to sit in a car for blacks.

Explanation:

Plessy v. Ferguson was a landmark 1896 U. S. Supreme Court decision that upheld the constitutionality of racial segregation under the "separate but equal" doctrine. The case stemmed from an 1892 incident in which African American train passenger Homer Plessy refused to sit in a car for blacks.