Circumstances or no, it's still verbal abuse. Yelling isn't going to make a person better, it just makes them stop trying. (Unless it's the military, but I didn't join for a reason.)
In all the raiding guilds I've been in, I have never dealt with a verbally abusive raid leader. And if I had one that did, I'd leave that guild immediately. I deal with enough verbally and emotionally abusive people in my life without getting yelled at over pixels and algorithms.