Plasma is superheated matter, and I'll agree that the heat dump would be considerable, but how much of that would be radiated "off the beam"? And, how much of that radiation would be heat (infrared), how much would be light, and how much would be "particle" radiation?
Fusion guns may be another matter, but I'm still not certain the would emit dangerous or significantly harmful (or potentially harmful) radiation off of its beam. I agree with incinerating things caught in the path of the beam, but how does that gybe with say a nearby tree getting its bark and leaves slightly scorched or irradiated by a fusion beam that passed within a meter of it?