Yes, but in medical and commercial applications they are operated by trained skilled people. They are carefully aimed first, and then they are activated in short pulses only while they are properly aimed, so there is a very very low risk of them ever being activated while they are not aimed at an intended target. And yes, a laser will not continue on beyond something that blocks its path unless it can burn fully through the obstruction but again, in commercial and medical applications they are not turned on and left on to burn completely through the target, they are operated in short pulses to achieve the desired effect. In a lawn mower that uses lasers to cut the grass, it would not be guaranteed that it would be operated by a highly trained, much less highly skilled (hold my beer and watch this) operator, and it would not be guaranteed that it would only be operated in short pulses that would be reasonably guaranteed to only encounter blades of grass.Also remember that LASERs are use in surgery and all sorts of industrial applications, so the beam can be controlled and caught. It doesn't just continue on forever through other materials.