In the Dutch East Indies, Dekker, then still in his twenties, started a career as a journalist, first in Semarang and later in Batavia. There he worked with Indo activist Karel Zaalberg, the chief editor of the newspaper "Bataviaasch Nieuwsblad", whom he befriended. On 5 May 1903, he married Clara Charlotte Deije, who would bear him three children. Unlike other people of European descent, he did not favour colonialism, strongly advocating self-management, and finally the independence, of the Dutch East Indies. This was prompted partly by his experience in watching the lives of plantation workers and partly by the discrimination he had suffered, through being only considered half-Dutch and a second-class citizen.