I believe the phenomenon of people buying houses "as an investment" is relatively new. People historically bought houses as places to live and have stability. They also happened to be a good investments but that wasn't their purpose. The change in primacy of purpose is pretty much a direct result of neoliberalization, which has been underway for decades since the post-WW2 era, but became much more normalized in the 70s/80s.
What I mean to say is that it's a current cultural trend, but hardly a law of the housing market. More problematically, if we make policy based on the assumption that people view houses as investments, it serves to reify that, rather than combat it.
I'd also be shocked if the market prices were primarily driven by your cited 65%. It's been a long time since our markets and policy-making machines have been primarily driven by the majority of the population. We are a democracy composed of powerful, minority (not speaking about racial groups but class groups) interests. Anyone blaming the 65% for our woes isn't paying enough attention to the absurd weight and influence exterted by only a handful of people and institutions.
I am someone with a life-long attachment to the island, and who is surrounded by homeowners both on and off of Cortes. They have seen their home prices go up by absurd percentages in the last 5 years, they all recognize it isn't right, they would not begrudge a market correction. Most people in my experience want everyone to live well and no one well-adjusted takes the "I got mine" attitude when it comes to housing. Meaning, a 20% drop in prices wouldn't cause them to lose their shit. Heck, they may even welcome it if it meant a thriving community. Money stuck in inflated property prices can't be invested in community, after all.