People type what they want into their computers. Their broker hits the trading floor and enters your requests on your behalf. Like cosmic said, the requests are controlled by your own parameters.
I do not not understand your initial statement. You want computers to decide investments? I don't think anybody wants to put their finances into a computer trading program, as they want to choose their own investments.
Corporations with shareholders often trade publicly as a way to get outside investment into their company. This is just how it is done. The investors can walk to the company on foot and buy shares, or if the company is trading on the exchange they can simply get their brokers to pick it up for them as per their order on their home pc.
The exchanges just save travel time for investors. If you want shares in microsoft you don't need to go to silicon valley.
Stopping companies from selling shares would only hurt businesses.
I am unsure what solution you are looking for?