Bro the point here is that whatever incredible developmental growth Gurgaon, NOIDA, Ghaziabad etc have achieved in the recent years is because these places are in NCR and bordering the National Capital. Developement has to go outwards because of space constraints within Delhi. As of the refugee slums of Delhi. Most of it (atleast 90%) were born after partition of the country in 1947. It cannot be helped because they had no other place to live. We cannot just throw them out. For more info you can refer to India after Gandhi by Ramachandra Guha.