This indeed is very sad, and it upsetting to see all this carelessness. Its not just the physical filth, but the mental sickness, the foul language, the open toilets everywhere, even in the so called most advanced city of Islamabad. I am visiting Pakistan after a long time and see alot of improvement in ISB, specially, in terms of road building, sidewalks etc. but the trash problem and open defacation in public (peshaab) is quite common.
It has to do with basic education. What is the solution, we should be part of the solution and do our part in keeping this country clean, atleast those of us that consider ourselves educated, we should also prove it with our actions, not just physical cleanliness but also mental and verbal usage should be watched as well.
It other countries, Pakistan that have been living, in "good areas" in USA, are very well behaved, sometimes even could be considered "model citizens", its all due to proper education, so its not that Pakistan are born to be careless, filth loving people, but alot has to do with education and application of what we learn and apply it physically in our lives. You feel good not only mentally, but physically you live in a spic and span neat and clean enviroment, free of flies, mosquitoes, and other diseases, with clean air to breath and clean calm environment to see as well hearing clean words and language. Isn't that what Islam also teaches us, 1/2 of our Imaan is cleanliness of body, mind, soul, spirit.