Bhai sahab! Your post can be divided in to two.
One: You are going to show Karachi/Pakistan had the skills/efforts and economic ability to survive because of locals. (Not true)
Two: Videos in which someone is is sad over the loss of “old Karachi”, who even has problem with naming a street of karachi as Zaibunnisa Street or mixed religious people not in Karachi anymore as well as no longer having having tram services.
All of these have nothing to do with the discussion but it is a good discussion and reasons can be discussed somewhere else.
I fail to see the relevance of these videos since you selectively showed videos of OLD Karachi. Unless somehow you want to show Karachi was ‘destroyed’ by Muhajirs.. 
The economy of Karachi has been the role model for many in early days and Karachi to date provides the economic support to Pakistan and** has it not been for Muhajirs, (those who migrated from India to Karachi) the country would have failed altogether from beginning. **South Korea adopted this model based on Karachi’s economy.
Read this my friend:
http://en.wikipedia.org/wiki/History_of_Karachi
Pakistan’s capital (1947-1958)District Karachi was chosen as the capital city of Pakistan and accommodated a huge influx of migrants and refugees from India to the newly formed country.
As a consequence, the demographics of the city also changed drastically. However, it still maintained a great cultural diversity as its new inhabitants arrived from the different parts of the India. In 1958, the capital of Pakistan was shifted from Karachi to Islamabad and Karachi became the capital of Sindh.
Large no. of rufugees migrated from India and embarked Karachi as the city of lights. Current modern Karachi is the result of efforts made by Mohajirs and their ancestors.[h=2]edit]
**Cosmopolitan City (1958-1980)
**This marked the start of a long period of decline in the city due to settlement of huge crowds of illegal refugees from other parts of the world. The city’s population continued to grow exceeding the capacity of its creaking infrastructure and increased the pressure on the city.
**During the 1960s, Karachi was seen as an economic role model around the world. Many countries sought to emulate Pakistan’s economic planning strategy and one of them, South Korea, copied the city’s second “Five-Year Plan” and World Financial Centre in Seoul is designed and modeled after Karachi.
Now, I have no problem in saying that the decision to move the capital of Pakistan from Karachi to ISB was one of the most stupid decision.**