A recent VillageSoup article reported on the formation of a new land trust in Midcoast Maine. Called the Midcoast Regional Housing Trust, the new entity (MCRHT) seeks to acquire or build housing for an overlooked sector called “workforce” housing, which is housing reserved for people making 80-120 percent of the area median income.

Land trusts are well known to this area as a conservation tool. Nonprofit trusts such as Coastal Mountains Land Trust, Georges River Land Trust, Maine Coast Heritage Trust and MidCoast Conservancy are trusts that buy land to protect it against development.

Housing land trusts have been around for a while. The Champlain Housing Trust in Burlington, Vt. is a well-known example. Housing trusts are somewhat counter to the organizing principle of conservation trusts. The former purchase and hold property in a developed state for the purpose of housing people and intend to preserve it as such.

The Champlain trust calls itself a Community Housing Trust. In that regard, I see the two types of land trusts as being related. They are both intended to “preserve” a community in the sense of holding private property to keep it from being bid up and locals from being excluded. Housing trusts work to make housing affordable to locals to live in, and conservation trusts work to keep land with affordable public access for basic recreation. At their best, they steward two types of local resources with the intention of community preservation.

The Midcoast Regional Housing Trust met with the Rockland City Council Nov. 7 to announce its intention to raise funds, in part through donations, to own and rent or sell housing to people in the “workforce” tier. From what I understand, the trust is related to Camden Rotary, perhaps sharing some common membership, and is sensitive to the needs of both workers in terms of supporting area residents and in terms of supporting local businesses.

Those who are concerned about a lack of affordable housing and advocate for more of it are often drawn to the idea of housing trusts as a possible path to decoupling local rents and home prices from upward market forces. The idea is that charitable organizations without a profit incentive can keep prices lower, and thus lower the cost to live in a community.

So, can housing trusts keep communities affordable places to live by keeping down rents and home prices? Unfortunately, they cannot.

What? You heard that right. Surely, the more housing dedicated to affordability, the more affordable the community? To understand why that isn’t the case, take a look at two very different cities to  understand the effects of land policy and ownership on affordability. They are Hong Kong and Buffalo.

Hong Kong is a major metropolis and trade hub. It’s also the world’s most expensive city to live in, according to CNN and other sources. It also, get ready for it, has more price-restricted housing than almost any other major city. An astonishing half of the housing stock is reserved for affordable housing. And yet it’s one of the most expensive places to live.

The huge amount of restricted housing is a primary reason Hong Kong’s housing market is so high, all other things being equal. This is because publicly owned housing competes in the market for land, and development density, restricting the amount available to the market. Sure, some people benefit, namely those who are lucky enough to find a subsidized unit. However, the rest of the residents have to compete over a smaller and smaller share of the housing stock. It has gotten to the point in Hong Kong where virtually no market housing is affordable to anyone on an income basis. Much of the private housing stock is owned by extremely wealthy occupants (income doesn’t matter) or is rented by corporations who absorb the cost as part of the employment costs of their workers. And don’t expect this to end anytime soon. The Hong Kong government has increased their target for the subsidized share of the market from 60% to 70%.

In contrast, look at Buffalo, N.Y. Sure, Buffalo lacks the economic dynamism of Hong Kong. But it’s still more affordable than Hong Kong relative to residents’ incomes. In fact, much of the housing in Buffalo, as in Detroit Mich., sells for less than its replacement cost. You’d be amazed what you can buy in Buffalo for $150,000. The reason that housing is cheap in Buffalo is simple. They have too much of it.

According to Macrotrends, Buffalo had a population of around 1,084,000 in 1970. Today, the number is just 884,000. That’s close to a 20% drop in 50 years. With a housing stock sized for over a million people, there are too many houses, or too few people, depending on how you look at it. And it’s kind of great.

These are two extreme examples but they both point to a very simple rule: the only way to have affordable housing for everyone is to have more than enough of it. Period. Trying to incrementally push housing units from the market into subsidized tiers doesn’t change the outcome. What it does do is create incumbent beneficiaries at the expense of newcomers. And that’s who is really hurt by exclusionary housing policies.

But what of housing trusts, can’t they do something? Not really. Imagine you created a new workforce housing model in Hong Kong. You either take a percentage of their housing stock away from low income households (an unenviable trade-off), or you absorb some housing from the market, which pushes up market prices proportionately. You just create a different set of winners and losers. But you can never make it fair to newcomers. There is a waitlist in Hong Kong of more than 250,000 people for subsidized housing, and that’s people who are already in Hong Kong. Social mobility suffers. Real mobility suffers. There is no meaningful “workforce” population in Hong Kong. The city instead has an enormous day worker population that commutes in from outside the city.

I respect and admire the interest of those backing the MCRHT or any trust to help shield people from home price increases, and to put patient capital to a social purpose. But there is only one way for housing trusts to effectively operate without further driving up prices and sapping mobility, and that is to build new housing, preferably dense housing, and not to compete in the market for the limited stock of existing homes.

What about buying older properties, fixing them up, and keeping the rents down? This also they should not do. The supply of existing, gently worn and functionally obsolescent housing is a precious resource I call Naturally Occurring Affordable Housing (NOAH). A well-intentioned party may say, buy a unit in sub par condition that’s rented for $650, make some repairs and put it back on the market for $950. Sure, $950 sounds good compared to a market rent of $1,500. But the other side of the coin is you just raised one household rent from $650 to $900. Are you sure that’s the right move? Might be better to buy a unit renting for $1,500 and lower the rent. But now you just took a unit out of the workforce tier and moved another household’s rent up the ladder. And so on.

This is why it’s so important for the community as a whole to build housing and not to obstruct or prevent via zoning and planning the construction of new housing. That new housing proposed across the street may not be your kid’s new home, but it is, in principle. Because by accepting that new home, you’re making a slot somewhere for someone’s kid who wants to stay in or move back to the area. Maybe even your own kid.

So do the right thing — let the new land trust build a home across the street.

Michael Mullins holds an MBA from the University of Chicago and an MS in Real Estate Development from MIT. His business, Cranesport LLC is based in Camden and he lives in Rockland.