Like the dry stone method, building walls or repairing walls with brightly coloured Lego might not be that crazy. It makes it possible to build with a certain amount of flare and flexibility. More importantly, if you have to, you can take your work down whenever someone in authority comes along and tells you it's in the wrong place or that it's a safety hazard.
Concrete cement is less useful. It smears, cracks and is more dangerous when it falls off . And if it doesn't fall off, it clings so hard to surfaces that to chip it off (to repair the damage it's done to brick and stone) is almost impossible. , Plus, if those in charge were really honest, compared to Legos, it is really much more of an aesthetic 'hazard'.