And once everyone had a replicator - everyone would replicate the newest, coolest, best car.
And nobody would pay for it.
And the people who design cars wouldn't have money to keep designing cars. And all of the advancement and innovation that we've seen since the first car and now would grind to a halt.
Abundance is the enemy of profit. Scarcity is profit's best friend. Economically speaking I agree with you, however if we can create the technology to produce everything in great abundance, we're going to have a lot of bored engineers wandering around. After awhile, innovation is going to explode. You can't motivate engineers with money, they motivate themselves by tackling difficult problems. Next thing you know, all of the necessities of life will become completely automated. Humans will become free from the shackles of a profit driven society; where people have to work to survive.
If I'd known computer science was going to be like this, I'd never have given up being a rock 'n' roll star. -- G. Hirst