That kind of illustration is called VANDALISM. Yes, its true that in some countries there are some designated freedom wall. But usually the "art" drawn or painted on the wall has some themes. In fact in some countries the outside walls along the gate of schools and even some government offices are often painted by students. The murals were completed through an organized art competition participated by primary or secondary students. You can see that there is a certain theme on the artwork. The murals often contains theme about peace, nationalism, environment, future visions, etc.
I do agree with Brother's thakek, If the Lao's interior-department allow the creative mine kids or adults to do it.They need to create a special zone for the Art, Not at (KUM-PEANG-WAT) or most important-departments, Example; I believe there's a lot of real dirty-Kum-peangs around Vientiane frefecture. so the Artist can use green-works products to clean up the walls or Urban landscapes. or they can use a friendly enviroment products for advertising or draw to promote their company's name something like that.for Instant Laos Airline, Lao's construction company, and Lao websit corp, so on.. et. this is was I've seen in Eruopean Artist do. specially in the NY city commercial area. they even award winners at the world's biggest competition for advertising creativity..