By others I mean whoever you have trusted to care for your child.
I've heard so many times, "no one lays a finger on my kid but me".
But you trusted them to step in as your proxy. So why is it that you can spank but the person you left him with cannot?
I have never heard anything of the sort from families that don't use spanking. I've never heard, "no one gives my kid a time out but me!"...
I think deep down all spankers know what they are doing is very risky to their childs well being. Otherwise they wouldn't mind if someone else used the same punishment that they use.