I am sorry. My explanation is very easily understood in concrete terms.

We give markets liquidity. Market liquidity is a market's ability to facilitate the sale or purchase of an asset without a drastic change to that assets price Bankers give markets liquidity by quickly taking advantage of price discrepancies. Arbitrage. Sometimes a purchase or sale is just speculation, the important thing is there are buyers and sellers available.

This liquidity allows for efficient allocation of capital. If products are priced according to market (due to liquidity) then capital is distributed in an efficient way. The safe investments are priced safely, the risky investments have their risk built into the price. Rewards may be correlated to risk. Good and bad business ideas are priced accordingly.

Efficient markets make everyone more wealthy. Everyone becomes more wealthy because efficient markets reward good ideas and punish bad ideas. For example, if somebody finds a way to make an aluminum can for 1 cent cheaper at the same quality. The market will reward this innovation and give businesses a chance to adopt the innovation. When companies adopt this advantage, prices for canned goods can be lowered. Given the the number of aluminum cans sold, this saves consumers millions of dollars a year. Everyone's dollar goes farther, therefore everyone is wealthier. Consider an inefficient market. There is corruption, insider trading, and rent-seeking behavior in general. You may argue that these things exist anyways, but you must agree that efficient markets fight against negative phenomena.

Analogies do a disservice to the complexity of the issue. Your analogy is especially outrageous. In reality, a President had the noble goal of allowing people to achieve some semblance of the "American Dream" by encouraging home ownership. His policies, which were continued by the following president, allowed consumers to purchase home for very little money down. People bought these homes anyways because they thought the asset they were purchasing (their home) would appreciate. Consider your same outrageous analogy with the banks as the wife and the "greedy" consumer (obviously consumers are not greedy for wanting to purchase a home). Customers abused the trust of the banks by buying homes they could not afford in a down market.

With regard to your last paragraph, if you can't see how important "investors" are to a modern economy then we really have nothing to talk about. You are either naive or being purposely obtuse. Investment banks, who I am assuming you are referring to, play an incredibly important and necessary role in our society.

If it is any consolation to you, I am billing a bulge bracket bank an obscene hourly rate to talk to you on reddit.