That's an interesting theorey. If it's correct that could explain it.

But, I just checked the demographics in Massachusets in the 1800s and it shows that there were 0 slaves. And it looks like minorities were in very very small numbers: https://en.wikipedia.org/wiki/1800_United_States_census

I don't think the labor supply of oppressed minorities was influential enough to drive down the cost of labor. Yes, for railroads sure but not for construction of buildings.

Are you claiming there are no other sources of price changes between now and 200 years ago than the social changes for women and minorities? And that the changes from the last 50 years or so caused the 6x price increase in housing?

Maybe that would be an explanation for USA, except that the same phenomenon occurs in many other countries, all over the world, where the current generation is no longer able to buy houses as easily as their grandparents, even if in those countries it cannot be said that 50 years ago or 80 years ago there was any kind of systematic oppression of minorities and women, which could have affected in any way the ratio between house prices and salaries.