With today's technology there really should be no reason we shouldn't be able to buy and sell stock at "book" directly through an exchange, except that it could end up having the volatility of the crypto market (which would be bad for the firms and the rich).
Instead of brokers, we should have regulated exchanges and anyone should have access to the exchange. If "XYZ corp" is trading at $1, I should be able to buy a share for $1.02 (assuming a fair transaction fee) the same way I just bought 499.8 ADA for about $15US the other day. Conversely I should be able to sell my shares at book through the same exchange.