Thoughtlessly saying "citation needed" is a recipe for an insidious confirmation bias. It is always intellectually lazy, in the same way that blindly accepting provided claims is intellectually lazy: it allows the reader to avoid thinking about the claims in question.
Citing a study is not a panacea for bad ideas, and lacking citations is not a death sentence for truth. Hacker News saw an article just the other day on how many conclusions drawn by science are incorrect. Don't be so eager to avoid thinking critically that the presence or absence of a citation dictates your response to an essay.