People who claim that others do not laugh enough, e.g. "stop being so glum, chum", "don't be such a sourpuss", "lighten up" etc may say that to encourage the other person to smile and laught because smiling and laughing are really just methods/means of displacing fear. e.g. tribal Africans who smile and joke almost compulsively because, they said, that life was hard (which is entirely understandable in the bush where a fatal hunting accident is only a moment away) [this was scene on either an episode of Ray Mears, or Bruce Parry in a south central, or south central-western African country, whose name totally escapes me].
The facial expression of smiling is also similar to one displayed when someone is overcome with fear ie eyes wide open, mouth either open, or facial muscles retracted - which displays the teeth. Smiling is also more commonly used by children and infants, who lack the developed mental faculties to overcome fear by use of reason. Thus, smiling is, a natural defnce mechanism used by alkl humans, and possibly primates and other mammals, to displace fear.
Those people who thus enoucarge others to smile are just encouraging them to revert/regress to a child like mentality; which is really just a means of subordinating others by subtle, underhand, methods. i.e. by dishonest means.
Lie: "Smiling is good, it shows other people that you're happy."
Truth: Smiling is a natural and instinctive means of counteracting/displacing fear.
Lie: "You should smile it makes other people feel good." [a basic premise is that smiling is a positive behavioural trait.]
Truth: Smiling to other people shows that you are fearful, possibly of them. Thus encouraging you to smile simply subordinates you relative to them. They want you to fear them, and not be a threat to them.
That's what smiling does to you. It subordiantes you relative to others. Anyone who encourages it wants you down in the dirt, subordinate, dumb, and childlike. Thus highly malleable for use by them at their pleasure.