I generally have quite aloud and boisterous voice, so even when I am not shouting people think I am !
I do have a bit of a temper, but have done wonders in deliberatley controlling it with DS ever since he was born.
Although my parents did not shout or hit us, I remember many of my relatives did, so I remember lots of shouting and throwing insults about at large family gatherings, which always scared me as a child and I would run for cover.
I have shouted at my toddler a few times (usually on days that I am really sick or really, really tired) and hated myself for it because he is so small and looks so startled when I do it.
I think the problem comes in when you do what my sister has been known to do, shout, then a small smack, then child cries, then she picks up and cuddles and kisses ! What a way to confuse a child !!
I don't agree with shouting as a form of discipline, but all I would say from what I have seen is if you are not consistent, then it's totally counterproductive.