Since it is clear that nations
can refuse to ratify a treaty with terms that are reflective of customary international law,
it is difficult to understand how or why international law would obligate them, when they
do ratify the treaty, to accept the treaty in its entirety.
Moreover, such a requirement
would have undesirable consequences for treatymaking. Given the amorphous nature of
customary international law – a point discussed below – it will often be difficult for
nations to know, when they ratify a treaty, whether a particular provision is reflective of
customary international law. A rule that outlawed reservations to all treaty terms
reflective of customary international law would thus create substantial uncertainty about
the validity of treaty reservations and, more broadly, about the status of treaty
relationships.

Спасибо ребята!