I am in favor of looser zoning laws and generally consider myself a YIMBY. However, I wouldn't say it is good politically to only support local low-income housing conditional on the fact that there is no negatives. I think that is the best policy but also acknowledge that there will be some tradeoffs.

As others have said I don't think looking at home values in major cities like Boston or Seattle is that interesting. Cities are used to having very rich areas next to poor ones. I grew up in a town of about 20,000 that had close to no housing that wasn't zoned as single family. As a result, the median income was very high, property taxes stayed extremely low as a percentage (since everyone was contributing a lot), and the schools were considered great despite people not having to pay a lot in taxes. The neighboring town had higher taxes (because the median property value was significantly lower) and the schools were known to be bad. I wish there was more state level funding at the time - but there wasn't and don't think there is now.