The government didn't FORCE the banks to do this. Many of them eagerly did it on their own, because they hoped to make big bucks on mortgage backed securities.
To be fair to those who want to blame Uncle Sam for what the private banks largely did on their own, the roots of the 2008 financial meltdown are complicated & controversial. There are a good half-dozen to a dozen major explanations of the crash that respectable experts have published in the past few years, and it's easy to see why many people don't understand the crisis..
One recent book that explictly discusses the community reinvestment angle, however, is "All the Devils Are Here," by financial reporters Bethany McLean and Joe Nocera.
What McLean and Nocera note is that the "securitizing" of mortgage loans had already become an attractive and seemingly proftable business by the early 1990s, when the private investment banks were eager to get into the business.
However, during the late 1980s and early 1990s the government-chartered but private owned mortgage leanders Fannie Mae and Freddie Mac had a virtual lock on the marketing of the most attractive mortgage-backed securities. They vigorously fought against efforts by the biggest Wall Street banks to take the business from them, too.
By the mid-1990s, therefore, most purchasers of mortgage-backed securities greatly preferred to buy from Fannie & Freddie when they could, and this meant that Fannie & Freddie traded in the vast majority of safe mortgage backed securities. The central role of Fannie & Freddie meant that big Wall Street banks were afraid of being squeezed out of this lucrative market.
What eventually gave the Wall Street bankers with no federal charters a promising way to get a piece of the securitized mortage business, though, was the growing popularity of securitized "subprime" mortgages.
In the beginning, anywayl, it was only home buyers with good credit histories and adequate incomes, buying conventional 30-year fixed-rate mortgages, who qualified for Fannie Mae and Freddie Mac mortgages. If you didn't make a large enough down payment, or if your income wasn't high enough, or if you didn't document your income well, you couldn't qualify for a Fannie Mae product.
But private mortgage lenders initially had the advantage in writing up "subprime" or "alt A" mortages -- mortgages made to people with bad credit, or with inadequate income levels, or with dubious or non-existent documentation to prove their qualifications for mortages.
To a large degree, therefore, private Wall Street lenders with no government backing plunged into buying up "subprime" mortgager from some fairly sleazy mortgage companies exploiting the bottom of the real estate market, and eventually Fannie & Freddie followed the Wall Street banks in relaxing their lending standards and buying securitized "subprime" mortages themselves -- before the market collapsed on everyone, of course.
Thus it was the banks themselves who raced to make risky loans, and to trade in dubious securities based on those loans. It wasn't the government taking the lead.
Apologists for Wall Street, and professional haters of government housing programs of all kind, naturally have tried to distort this history. But those are the facts.