"problems really started when the US allowed (and we followed natch) its normal banks that deal with 'normal customers money' to start investment arms. It was all this massive speculation with money borrowed from Peter, Paul, Mary, Mary's friend in the next street, her cousin and her sister's cousins best friend to buy stocks in companies that were not necessarily acting in the best accounting practices (Enron etc) that have led to such problems."
I'm not quite sure what you mean by this, tbh.
I'm assuming you mean "normal customers" = commercial banking customers, and "investment arms" to mean investment banks or other financial institutions that acts as stock market brokers.
My objections to the statement above are:
(1) Commercial banking customers are very often also investment banking customers, for the simple reason that many people with some money in savings diversify - some money in long term saving accounts (with minimal interest rates), some in bonds (higher returns than saving accounts but low-risk), and some in the stock markets (potentially high returns with high risk). This is entirely normal and is not a nefarious development whereby the whole financial system has been led astray.
(2) Commercial banks don't as a rule start investment banking arms (or build any other subsidiary with a different business) with deposits from commercial banking arms. If you have ever signed the many contracts needed to open an investment banking account, you would remember that these are very different than those necessary for a simple deposit account. Clients open separate accounts with investment banks, which they authorize for investment banking transactions. (Or am I misunderstanding what you said?)
(3) Related to (2), it is not at all the ownership structure of commercial & investment banks (whether some are owned by the same entity) that caused the credit crisis. In fact, the first dominos to fall were purely investment banking firms such as Lehman Brothers and Bear Stearns, and not those that have both commercial and investment banking arms like Citibank.
(4) Investment banking is not "massive speculation", although some adrenaline junkies / gamblers might use it as such. Just like the futures/options market I gave very legitimate examples for earlier, stock markets = capital markets are there so that companies can raise money for various reasons that don't involve begging a bank for money and having to pay interest on that money. I'm sure that this was covered at your university courses on the subject.
(5) Enron is a criminal problem, not a systemic one. Its management were crooks who were hiding their criminal activities. I'm not sure you can tie such criminal activity (which you have to admit is few and far between) to the financial crisis that covered the whole world.