Actually, Lasers are insanely effective at destroying missiles, mortars, and even tanks. The Airforce has a laser mounted to one of their large aircraft, forget which. Years ago it got tested on a tank and fragged it. Since the US military always goes for air superiority first, there isn't a lot of threat to such a gnarly weapon system flying high in the sky and sniping enemy tanks, emplacements, bunkers, etc.
It wont be long before a tank, with a built in generator, is feasible. The Laser system the Army is using, is actually not that big. Nor is the Navy's. It could easily be integrated into a Tank-platform. Supplying it with energy is likely the biggest drawback to a Laser-tank, at the moment.
This one shows the army version.