I object to the presumption that young people are only interested in pop music.

presumption 是由动词 presume（假定、推测）加上名词后缀 -tion 构成的名词，意思是"假设、推定"。这个词带有"未经证实就做出判断"的负面含义，所以常翻译为"臆断"或"武断的假设"。