I also lived in Karachi, and I always had proper functioning fresh air vents in all my cars, yes you do get dust and yes you do get dry leaves, but that happens everywhere, Even here in houston dry leaves, bugs, pine needles, junk etc. get trapped in the fresh air intake ducts and also water drains which create problems like mold, smell etc. This is the reason we have preventive maintenance - its even in the service manual of every car to remove tree debris and dust from the cars crevices otherwise a myriad of problems arise.
Also if you dont have fresh air circulating in the car, you will get woozy if you drive too long, and over a matter of time your car will start to smell like "bad breath"