However, I think you are reading something into this that isn't there. Here is a link to Fidelity's description of their own dark book: https://www.fidelitycapitalmarkets.com/crossstream.htm
The purpose of these dark books is to hide the INTENTIONS (future tense) of a large institutional investor, who wants to buy or sell a large block of stock, say one million shares. If this transaction were put into the public market place, it would move the price of that stock dramatically, and increase volatility way outside of the normal envelope. It would also create some really bad fills for the institutions involved. As a result, institutions have always traded with each other, away from the exchanges, as much as they could. There is nothing new here
The complaint seems only to come from traders who use liquidity models in their trading methodology. They don't want these trades kept secret! How awful! This is like saying, I don't know how much I should spend fixing up my house unless I can know how much money my neighbor has in his bank account. People who want to know other peoples’ business usually have their own agenda, no matter how much they tout transparency.
People are making comments that these dark pools allow for tax-evasion, commodity manipulation, the hiding of troublesome transactions, etc. This is all nonsense. While the transactions take place away from the exchanges, they must all be reported after the fact by the institutions (pension funds, mutual funds, insurance companies, trust funds, etc) in their required reports to the IRS, SEC, their shareholders, etc.
I see no Enron-like mechanism here to defraud. I think people are simply misunderstanding something with which they are generally unfamiliar.
Institutions do not mind going public when volatility is in their favor. Institutions can announce certain big transaction in public when you know doing so would increase value of your stock holding dramatically. However, when going public would trigger unwanted sell-off. they may want to do it in secret in a dark pool.
This may have been going on in the past. However, with sophisticated software backing it up, now its trading volume can markedly increase in volume. There are also more than one such venue. Each does their own transaction and we have essentially one public market and several hidden markets of significant size. They may all set different prices for the same item. Price as market signal lose its function. Market confidence will plummet, because nobody knows exactly what the real price of certain item is. Actually, I suspect this is why they try to get feelers out to other venues(dark or public) to find out what the real price could be.
The long-term consequence would be mistrust of public market. Prices people see in NYSE could be actually a mirage. The public stock market becomes useless.
Besides, being so closed, wouldn't it be easier to conceal certain information from regulators or public?