Who is going tell these people "No"

So do see the problem? Who is allowing these people to build in unsafe conditions?

 

A landslide in Santa Tecla, El Salvador, following an earthquake in January 2001. Citing damage from the earthquake, the American government permitted Salvadorans illegally in the U.S. to remain. Credit La Prensa Grafica, via Associated Press

 

In the City of Edmonton, there is similar problem along the river valley, but the problem is the people wanting to build on the slopes. So can a engineer say no, it is not safe? Or will the land owner just shop it around to find others who will say it is ok?