I don't think this strategy would work. Even if young people decide to forgo buying housing, they still need a place to live. Ergo, they will rent. Which will mean demand will still be the same. 

Housing is expensive partly because demand is always constant. No one can just abstain from the market.

yes but

(i) rent demand != buying demand; the former sets a floor on the latter but the latter can fly high on its own
(ii) you can abstain from the market on the margin by living in smaller or less-prime-location homes, not buying second homes... this can make a big impact

agreed. down-scaling en masse can be an effective lever to force prices down, wether you own or rent.