Ugh - I have a specific dislike of that sort of sentiment.  Pure idealism.  Pretend reality doesn't matter and focus exclusively on the ideas in your head.  Just a variation on magical thinking.
It's pretty much the basis of Boris Johnson's whole approach to government.  Just tell everyone to maintain an optimistic frame-of-mind and Brexit will magically work out and the pandemic will go away.  The CBT approach to politics.  Beloved of ultra-privileged public-school types, for whom things have always mysteriously worked-out, so they assume that is a universal rule for everyone.
(Or am I'm over-reacting and going full P&N to what is likely just a throwaway quoted song-lyric?)
		
		
	 
Your sentiments may be valid in terms the relationship between some authority PR'ing the collective, but on the level of a individual person's internal outlook, the lyrics makes complete sense. 
I do believe those who are mentally ill have some form of distorted perception. 
Anorexics are an easy-to-understand example. To us, the outsider, they are clearly unhealthy and a bag of bones. But when they look in the mirror or take other measurements, they considered themselves fat and not beautiful/manly depending on the gender. What they see is not what outsiders see. 
The difference between just feeling down or having a deep-seated misperception often can be discerned by the response. A person who is in a state of chronic misperception will 
not respond well to positive comments intended to lift them from whatever makes them feel down. 
I mentioned Brahms in this thread because he was an insecure person who responded in such a manner; Schumann praising him only made him more nervous, and he was an extreme perfectionist. Apparently, his appearance also led to insecurity, being a prolonged baby-face similar to Selena Gomez.