Um, actually I’d say it is the responsibility of all scientists, both professional and amateur, to point out falsehoods when they’re uttered, and not an act of smugness.

[um], has contexts but is usually a cue, that an unexpected, off the average, something is about to be said.

[actually], is a neutral declaration that some cognitive structure was presented, but is at odds with physically observable fact that will now be laid out to you.