I'm not following your logic here.
You claim the real estate bubble was caused by capital gains tax rates?
I think he's refering to the theory that too much money in the financial sector helped fuel the mortgage bubble. Short version: At the start of the century, there were a lot of people with more money than sense.
Long version: At the beginning of the century, there was more money floating around the financial sector looking to be invested than there were actually worthwhile things to invest in. It was like a hundred millionaires all trying to buy the same fifty shares of a company. No matter how much people are willing to invest, there are not enough shares to go around. Mortgages were historically profitable, but buying and selling individual mortgages was way too much paperwork to justify getting into the business directly.
Then someone came up with the mortgage backed security, where they would take a bunch of mortgages, bundle them together into a security (a Colatoralized Debt Obligation, or CDO for short), and then sell that. This solved a lot of problems for investors, who only had to own one thing, and since there were many mortgages in the CDO, it had diversifiction built in.
Mortgage brokers took all the mortgages they had made to responsible lenders, bundled them together into CDOs, and sold them off. The securities were a big hit, and investment firms went to the brokers to buy more, since they still had lots and lots of money to invest.
But the brokers had a problem. They had already bundled and sold off the mortgages that they had, and everyone who was a good credit risk who wanted a mortgage already had one. So the brokers lowered standards a little bit, sold some more mortgages, bundled those together into securites, bought some good ratings from a ratings agency, and sold off the securities.
Investment groups went back to the brokers again, and well, we all know how the story ended...
Even then, the mortgage crash probably wouldn't have been nearly so bad if someone hadn't invented the "Synthetic CDO". Basically, several people were looking at declining mortgage standards and saw how it was going to play out, and decided to short the market by buying insurance on the mortgage backed securities. They found some suckers who were willing to sell them insurance at stupidly low rates, this was called a "Credit Default Swap".
The Credit Default Swap consisted of the smart people at one end, who paid insurance premiums against mortgage backed securites failing, and the people at the dumb end, who cheerfully counted the money they were getting in insurance premiums, blissfully unaware that the housing market was going to implode and that they were going to have to pay out.
This probably would have stopped at some point when the people at the dumb end wondered why people were so eager to buy insurance from them and thought about raising their rates at least, but then some genius had the greatest idea of all. Why not take the dumb end of these insurance bets and bundle them together like they did for the mortgage backed securities, and sell them off to investors with too much money on their hands? Thus, the "Synthetic CDO" was born.
It created a similar feedback loop as we saw in the mortgage backed securites. People bought insurance against CDOs failing, the insurers bundled the bad end of the bets into Synthetic CDOs, bought AAA ratings from rating agencies, and sold it off to suckers.
But the Synthetic CDO was different from the mortgage backed securites in one important aspect. A mortgage backed security was backed by mortgages, and there are only so many mortgages you can sell, no matter how far you lower standards. A Synthetic CDO is backed by insurance policies, and there is no physical limit to the amount of insurance you can sell. All you needed was someone willing to bet that the housing market would tank, and there were plenty of those floating around especially when the insurers were selling bets at 80:1 odds. And thus, a trillion dollars of loss could be created out of thin air.
When the market collapsed, the smart money people called up the people holding the insurance policies and asked for their money (as one caller is claimed to have said, "Dude, you owe us one point two billion dollars."), and everything went to hell.