Cambridge has been changing rapidly over the past 10 to 15 years. Since the economic slowdown of the 1970s, former city manager Robert W. Healy’s constant focus on the bottom line has made us comparatively quite wealthy. But with more than 20,000 residents having been forced out of Cambridge, clearly something is wrong.

Cambridge is a great place to live. The universities and rich culture make this city very attractive. Empty nesters have been flocking here from their suburban homes; students stay after they graduate. Its proximity to Boston, attractive cityscape, quiet neighborhoods, great restaurants and well-funded public schools make it a really nice place to live. Add the city’s commitment to human rights and other issues, and it’s not surprising that so many people want to live here. But besides Cambridge’s superb quality of life, the one factor that has always driven people to come is jobs. Cambridge has attracted tech, biotech and pharmaceutical research companies, offering them an unmatched pool of highly educated professionals and support staff. Long gone are the days that we needed to attract business; now we can’t build fast enough to provide the insatiable hunger for commercial space.

It wasn’t long ago that Cambridge had been in an economic decline. The 1950s saw a sharp decline in domestic manufacturing, leaving the city with numerous abandoned factories; it wasn’t until the 1980s that things began to turn around. The city pursued corporations to locate here, offering various incentives, and by the 1990s we could see it working in areas such as Kendall Square, Fresh Pond and NorthPoint (now Cambridge Crossing). The city’s rezoning encouraged greater commercial density, and requests for even more were typically granted.

Back in the 1990s, the Cambridge Citizens for Livable Neighborhoods estimated that 1 million people wanted to move to Cambridge. By 2005, with the rapid expansion of biotech, the number has undoubtedly grown.

These changes in Cambridge’s real estate market made real estate agents giddy. Investors were eager to churn properties. Developers looked for zoning nuances to turn simple three-family, middle-income buildings into six luxury condos. Everyone thought they struck gold. Everyone – except the 20,000 who were forced out of their apartments.

“Build, build, build,”  the industry shouted, claiming that the only solution was to harness the economic power of supply and demand – as if we were selling eggs. Building a few thousand high-priced condos with the belief that the law of supply and demand will somehow alleviate the problem is naïve. We cannot (and should not) fit 900,000 more people here. Furthermore, this strategy hasn’t worked anywhere in the United States.

Encouraging ever-increasing commercial development has exacerbated the problem. Traffic getting into Cambridge has become horrendous, and new employees who try to commute want to move here. The enormous influx of high-salary professionals has driven housing prices to ever-increasing levels. This places our housing stock beyond the reach of anyone who doesn’t earn six figures.

We also should not lose sight of what we want to preserve in our city. Do we want a Manhattan-style urban environment? Do we want round-the-clock gridlock traffic, dangerously crowded trains and overburdened city services?

Building more affordable housing is an admirable goal. But so far, we’ve added only a tiny handful of units. For every one we add, we’re losing five to 10 existing units. For example, while some celebrated the City Council’s “deal” to add 24 affordable units at East Cambridge’s former courthouse, they failed to see that this 500,000-square-foot commercial development will employ 3,000 people, approximately half of whom will seek local housing. The potential loss to middle-income people: 1,500 units.

At the same time, developers are making millions upon millions of dollars. It’s quite obvious that we’re being misled. The law of supply and demand isn’t applicable to housing, especially when the disparity is so huge.

Our leaders have a choice to make: Either Cambridge can continue with the same clearly failed policies, or we can be bold and adopt policies that stop or slow the rapid erosion of our middle-income housing. We don’t have to succumb to the developer-enriching real-estate grab, destroying swaths of our neighborhoods, choking the streets with never-ending traffic, placing even more people on our over-burdened transit system. We can do better.

Phillip Sego, Norfolk Street