Quote Originally Posted by MFauli View Post
Also, how is it smart to LIE to everyone?! What will they do when they find out the USA aren't there? Even if they don't return to Tsukasa, they'd rightfully be pissed at Senku.
Gen and Senku discussed how the lie will backfire on them either way, episodes ago.

The point is to end Tsukasa's influence and return to an innovation and science-based society that intends to save every petrified human on earth. "Might Makes Right" is currently winning, and Tsukasa intends to kill off all the older people for good so that his "pure" society is all that remains.

This has been explained.