If disfluencies appear to generally help communication more than they hinder it, why are they so stigmatized? Writer and linguist Michael Erard argues in his book Um… that historically, public speakers have been blissfully unconcerned with disinfecting their speech of disfluencies until about the 20th Century—possibly because neither hearers nor speakers consciously noticed them until it became possible to record and replay spoken language in all its circuitous and halting glory. The aversion to disfluencies may well have arisen from speakers’ horror at hearing their own recorded voices. Erard suggests that the modern repugnance for disfluencies is less an assessment of a person’s speech than it is a “deeper judgment about how much control he should have over his self-presentation and his identity.”
Source: Your Speech Is Packed With Misunderstood, Unconscious Messages