I think the best counter to becoming desensitized or depressed is having an over arching sense of mission and identifying your work with a cause for good that is greater than yourself.

take ER doctors. they daily witness human trauma far worse than viewing horror show videos and images. do you ever hear about ER docs who become depressed or mentally ill from being exposed to so much horrific human suffering? Doctors have a personal sense of doing good in the world through healing. They witness so much trauma that they become so desensitized that non doctors often criticize them for seeming so detached and for treating human bodies like mechanistic processes. But doctors have to be somewhat detached in order to do their jobs well.