> In other words, the enforcement mechanism has to come from those that opt-in to that organization. i.e: through mutual agreement.

Tell that to the germans who were hanged at the nuremburg trials. They certainly didn't consent.

You are right to a certain extent, that enforcement requires agreement or force, but at the same time the general rules and procedures of international law do have some force to them. They have this force because they are widely agreed on. This includes Israel which broadly agree all these things are illegal, they just take issue with that specific court. However their donestic courts recognize all the things the icc prosecutes as crimes locally broadly speaking. (Well there is some dispute over what forced population transfer means, but that isn't one of the crimes in question for this warrant)