Handholding and Singing
Symbolism, Imagery, Allegory
In the book, the handholding and singing isn't there just to give more immature readers a case of the giggles over all the cooties that abound in the scene.
Though it may look silly (and a bit too touchy-feely), the idea of the Whos coming together and joining hands is actually a Christmas metaphor for the ages. Their handholding and harmonizing solidifies the fact that they are a strong community. Together they can rise above any pesky meddling from the Grinch.
Archie Bunkers of the world, take note: Christmas isn't over for them at all; in a show of defiance—and of strength—they continue to hold hands and sing while the befuddled Grinch stands atop Mt. Crumpit, wondering why they aren't sobbing and blubbering and sniffling away.
How's that for a peaceful protest? They're just missing the flowers in their hair.