Well, the 1923 population exchange between Greece and Turkey was arranged by the European Powers under The Treaty of Lausanne. Kemal Ataturk and Elefthertios Venizelos-(who I believe was the Greek Prime Minister at the time), were not the Prime Arrangers of this population exchange.
One has to understand the very tense atmosphere that existed between Greece and Turkey at that time. Just a year prior to the Greco-Turkish population exchange was The Great Fire in Smyrna, which was the culmination of an ethnic and religious cleansing campaign orchestrated by Kemal Ataturk. The aim was to ethnically, as well as religiously cleanse the centuries old Greek-(as well as Armenian) Christian residents of the city of Smyrna........and it succeeded. In September, 1922, the Greek Christian residents of Smyrna were forcibly uprooted from their homes in Smyrna and primarily relocated to neighboring Greece-(particularly, Athens). (Note: Smyrna and Izmir, are the same city, though named and identified in different languages).
For the remaining Asia Minor Greek Christian population, continuing to reside in Turkey-(primarily near The Black Sea region) since the 1922 Smyrna Catastrophe, was becoming increasingly and dangerously difficult. The Hellenic presence in the Turkish Black Sea region in the early-mid 1920's, posed both a religious, as well as an ethnic problem to the Kemalists. They expressed a strong adversity towards the Greeks of the Black Sea both in terms of their Orthodox Christian faith, as well as their Greek ethnic identity. One has to remember that religion and ethnicity were intertwined and in many ways, were "two sides of the same coin".
The same was probably true for the Turkish Muslim population in Northern Greece, whereby the region of Macedonia had only been part of the Modern Greek nation-state for approximately a decade and Greco-Macedonian nationalist sentiments were very high at that time. I suspect that being a Turkish Muslim in Greco-Christian Macedonia during the early-mid 1920's, was probably quite difficult, due to the widespread nationalism within the region.
During the mid-late 1920's, both the English and the French Empires were filling in the colonial vacuum within the Eastern Mediterranean and Southern Black Sea regions and wanted to maintain a level of peace in this part of the world, due to its close proximity to both the Near & Middle East, which, at the time, were under the colonial auspices of both the British and French Empires. By religiously and ethnically homogenizing both Greece and Turkey, the Southern Balkan region would be somewhat pacified and the British, as well as the French spheres of influence in the Near & Middle East, would remain geopolitically stable.
The 1923 Greco-Turkish Lausanne based population exchange was a labyrinthine way of the European Colonial Powers maintaining peace in a historically tense corner of the world. It was also a devastatingly difficult transformation for the residents-(on both sides) to initially undergo and experience. Though as time progressed, many began to assimilate into their new homelands and joined into the larger Greek nation or Turkish nation.