I agree that force should not be of a physical nature, but that in order to be effective discipline needs to be clear, consistent, fair and relevant. It is important that rules are clear to all parties and that these are discussed in a calm way BEFORE an issue occurs (they can be established by reflecting on a better way to deal with an earlier issue, but should not be a 'knee jerk' reaction to a current event.)
I see force as the power to carry through with a consequence set up as a result of a misdemeanour. Idle threats or unrealistic consequences have no force to modify behaviour. Likewise, physical punishment does not teach the message of restraint, care and respect for others that we need to establish in our children.
Force also exists in each of the parties involved being 'on the same page'. Communication between parents, caregivers, teachers and home and school need to be established and maintained to make a message clear. It is very difficult to have effective discipline to prevent smoking in school if students are allowed to smoke at home. Force to me is unity and consistency, not physical harm.
I am not at all sure that I agree with this premise, especially if you mean physical force. However, if this is what you are supposed to argue, I would say that more force is necessary to teach children that their actions have consequences and that they are responsible for taking the consequences of their actions.
If a child misbehaves and there is no discipline or weak discipline, he or she is sent the message that actions have no consequences. If children learn that their actions have no consequences, they will not act in a responsible way because responsibility really means accepting the consequences (good or bad) of what you do.
Therefore, disciplining a child in a strong way (however you are defining that) sends a strong message and teaches them that they do indeed have to accept the consequences of their actions. By doing so (you can argue) you are teaching them responsibility.