before Bhai log came from Bangladesh and villagers and mountaineers thrashed it, Karachi was a city of a decent and educated population. In downtown Karachi, you could see Australians, Russians, Chinese etc in great number..but now you see all non-Karachi born people.
There 2 factual errors in your post.
1. People who came from Bangladesh mainly settled in orangi(biharis) and around lyari river (bengalis)in some places, they were very passive people, both the groups were passive, and never posed any threat. Although there are pick pocketer gangs operating from orangi but they are all non voilent, i.e. they dont cause any physical harm. Their areas are open and anyone can visit and freely roam around there.
2. About the villagers, from rest of Pakistan, yes they have caused problems, but its not their fault. They were raised in different environment, and they come to karachi because thatswhere the oppurtnities are. There will always be migration to commercial center of the country. But the number of people is the problem. And the only way to control this is to provide jobs and facilities in rural areas, most of them prefer living in open spaces rather the congested areas in karachi they end up living. The trick is to bring up the standard of living of rural areas, rather then bringing down the standard of living of the urban area to match the rural area(which is what ppp has been doing for last 50+ years).