BlackSwan, don't mind telling you that much of what you've posted there is a load of...Do you really think people betting/trading at that size is what kills market makers? Absolutely not - it shouldn't be unless the MMs are crooks i.e. they proactively bet against their clients.
True Marketmaking, which is what the SB companies are supposed to be doing is simply passing on the spread yet leaving the risk with the client. MMs are supposed to have a NET book on every stock/instrument which they then hedge or insure against and if they do this properly and manage it right, they'll always make money at a certain margin.
The problem is, the MMs are GREEDY and very much so. Their regular margin is NOT enough for the majority of them. They like to exploit their extensive inside knowledge of the markets to trade against their clients and grow their own accounts. There's actually nothing wrong with wanting to trade or even to use your extensive knowledge to your own advantage. What's wrong is trying to use this AGAINST YOUR CLIENTS to enrich yourself and that's where the jiggery pokery around execution and prices comes in. Many SB companies (not all) deliberately manipulate prices to the disadvantage of their clients. How many times do we experience slippage to our advantage?..did I hear never?
The issue of SB companies being 'glorified bookies', though apt, is flawed. They are SUPPOSED to be more than that. Why? because normal bookies have no real underlying market! They simply quote prices based on their OPINION. You are therefore ALWAYS trading against that opinion and nothing else. It is up to them how they then manage their NET book for profitability.
SB companies on the other hand DO have an underlying market which offers its own real world prices based on supply and demand and they are supposed to quote around these real world prices. Though there's a 'betting' layer on top of this trading market layer, that's really just a devise for the MAIN benefit of SB which is no CGTax.
The market element is MORE important than the betting element hence why SB firms are FSA regulated!