The cost of change is clear in this case: estrangement from the Ottoman Turkish literary and linguistic heritage, as well as estrangement from the Arabs and the Persians, as Atatürk's language reform purged a lot of Arabic and Persian loan words from Turkish,* replacing them by European loan words, obsolete Turkish words that were resurrected, loan words from other Turkic languages, and neologisms.
What was the advantage? It seems that there is none that couldn't have been had by simply modifying the Ottoman Turkish script to better signify the sounds of the Turkish language (especially of its plebeian dialects), since Turkey couldn't even persuade the Turkic-language-speaking ex-Soviet states to adopt the modern Turkish alphabet (though they all have made efforts to switch out of the Cyrillic), thus winning no pan-Turkic advantage even after the fall of the USSR.
* Even the teaching of Arabic and Persian was removed from the curriculum: "the study of Arabic and Persian as foreign languages was removed from the standard curriculum for secondary-level education in 1929" (Suzanne Wertheim, Linguistic Purism, Language Shift, and Contact-induced Change in Tatar, University of California, Berkeley, 2003, <http://ling.northwestern.edu/~wertheim/Chapter%202-%20Part%202.pdf>).
> As to headscarves I am not sure what it means to dismiss modesty-enforcing
> dress codes as 'western; but not 'modern'. Are we really saying that
> equality between the sexes is a western, not a human value?
If no one is forced by the state to wear hijab, it is not a code in a legal sense. Hijab that is voluntarily worn is merely a symbolic code, the same as any other gendered symbolic code of dress, behavior, etc.
Besides, all clothes, male and female, gendered or ungendered, have a function of enforcing modesty among other functions. Unless you are a nudist, what's the objection to that? A socialist is in favor of classless society, the withering away of the state, etc., but the building of a society without clothes has not been on the socialist agenda. -- Yoshie