I should point out residents near St. Camillus Church's proposed affordable housing development did have other concerns, mostly having to do with drainage, and so it's not just a case of NIMBYism. I hope that something can be worked out. But there are some other points as well.
To live in many parts of Arlington is to wage a neverending
fight against groundwater. I used to live on at the top of a hill and we'd still get groundwater in the basement ! (And we did keep water away from the foundation with gutter downspout extenders and all that. Other people in the neighboorhood has the same problem.) Perhaps as reasonably engineered solution will be found for the new housing if it actually goes through. I would also note that when it comes time to sell their houses, people are strangely reticent about talking about such problems.
A lot of people are concerned about density. There seems to be this illusion among some residents that Arlington is Dover. It is silly to expect that a development on a small piece of land has to be constrained to single-family home style -- that will chew up a lot of space. Instead, it would probably make sense to have townhouses. In addition, a smaller footprint on the land could help with the drainage problems that everyone is
so concerned about.