Respectfully, this is just plain incorrect. You're describing some situations that do happen and just choosing to ignore what happens the rest of the time. When demand precisely matches supply, you're correct--you need a matching engine to connect buyer and seller and no middle man/market maker need get between them. That also happens too.

Assuming that at some point bids and asks will line up and trades will happen doesn't a market make; that's the exchange's job. Making a market means being able to quote prices on both sides of the book and having inventory to trade at the current market price. Carrying that inventory has actual risk involved, and that's why it's not a free service that the exchange (or anyone else) provides. Market makers also get penalized by the exchanges if they're not making markets for some large percentage of the time that the products are trading.

Maybe a better way to look at it is that the exchange is there to match up buyers and sellers at the current price at a given moment in time. The market matches up buyers and sellers at the current price over a period of time. This market stabilizes the price over time. Demand and supply just don't line up perfectly like it seems like they should. That's the difference between the market and the exchange. If I'm buying a product now, I want an idea of the true value of it, and the less the price is whipping around waiting for demand to match the supply, the more I know what the current market rate is.

I'm not saying they're doing gods work, but to say that there's no risk involved or reason for them to exist is incorrect.

If you don't buy any of the above arguments, then I'm interested in your answer to the question of why the exchanges themselves pay market makers to make markets. If the current technology renders market makers obsolete, surely the exchanges would recognize that and keep the money for themselves, no?