Everyone having a copy of the whole blockchain is not needed. What you need is sufficiently distributed hashpower that no actor can perform a 51% attack. That's all.

Small-time users can use thin wallets; mega-power users can download the whole blockchain and spend whatever (in perspective, not super significant) amount of money they need for sufficient storage. Users in between can carry a reduced form of the blockchain that doesn't care so much about a full transaction log but accurately describes the state of every wallet's balance (thereby functioning the same from a "verify that they're not bullshitting me" perspective).