Is the second demographic transition theory a development idealism?

Lesthaeghe, R., 2010. The Unfolding Story of the Second Demographic Transition. PDR

In this paper, Lesthaeghe attempts to theorize the demographic change under the sub-replacement fertility, but he implicitly assumes, using a Maslow's framework, an inclination towards a post-material value (self-realization and autonomy) as a consequence of societal development. On the other hand, he also mentioned the strong family regimes in Southern European countries. Strong family regimes are quite comparable to that of East Asia, where intergenerational coresidence has been prevalent. The majority (approximately 70% or more) of never-married young adults stay in their parents’ home, and this trend has been stable over the past decades. These countries with strong family regimes often emphasize the importance of family lineage (ie in Japanese or jib in Korean), and eldest sons have long been expected to live with their parents after marriage, in order to maintain the family lineage. The wives of eldest sons are thus more likely than women married to second and third sons to coreside with their parents-in-law.

Based on this cultural context, the Japanese government recently started to promote three-generation living arrangements to "facilitate the flow and volume of intergenerational support" (Izuhara 2018). Behind the "re-familiarization" policy, some studies provided an empirical support a positive association between intergenerational coresidence and (1) mother's labor force participation and (2) additional childbearing. The relationship is also observed in countries with other family regimes, such as UK (Kanji 2017).

The role of intergenerational coresidence reminds me an assumed distinction between "traditional" and "modern" in family demography. As Thornton (2001)'s article revealed, developmental idealism influences our thinking about family formation in various ways. Except for a couple of scholars who strongly emphasized the inertia of Japanese family system, most demographers in Japan seem to be against the abovementioned “re-familiarization” policy, because it has been considered as the policy towards "traditional" living arrangement which oppress individual autonomy. However, living with parents after school graduation or marriage is not a "traditional" thing, or not limited to those strong family countries. Other affluent countries, where there has been a rise in cost of living and growing economic uncertainty, have seen an increase in Boomerang kids: adult children coming back to parents home after independence (Newman 2013).

Why did the second demographic transition theory pay a bit too much emphasis on individual autonomy and associate it with social development, while dismissing a potential importance of "traditional" living arrangement? Is this also due to the development idealism which labels free and equal family as modern and the modern family as good?