You would be absolutely correct, logically, if someone thought that it was the only effective form of discipline, that they would then, logically support a daycare provider to spank their child. In fact, I think that I have met people that actually hold this view.
I for one, or we(me & hubby together), use spanking as one discipline tool (among many) with our children, and neither of us would condone spanking in a daycare or teaching situation. The reason for it is this: we know ourselves, this is something we do before the Lord, we have a preplanned and consistent method for carrying out this discipline, as to end up as a positive experience and continuing closeness and bonding with the parent/child. The children already have a deep trust/love relationship with us. This is not the only form of discipline........many different reasons that our children aren't running from us for every little thing they do wrong, because they know they are going to be treated with love and respect.
No one else has this particular relationship with my child. They do not have the trust/bond that we do, it is inappropriate, therefore, for anyone to feel they can step into this place, using a form of discipline that needs to be surrounded by love and trust. To me, a child can easily, even if a daycare provider is loving, misinterpret this type of discipline. A child is very sensitive, and can pick up of these things that just "seem" out of line, not quite what they should be.
Not only this, but I don't trust that anyone else will really have the same standards that I do with following through with a spanking with my child. Even if their methods match with mine, I don't feel my child would feel comfortable with it (someone else spanking them), nor should they.
My opinion. Hope it isn't too jumbled, kinda rambled.