Unless the inherency evidence overwhelmingly indicates that the only barrier to UNSC approval is US support--or better yet, a thread of US veto. The flaw in your argument above is that the US is a member of the UNSC, and as such could, in fact, be the inherent barrier.
Furthermore, no one is talking about fiating the UNSC...only running an argument that maintains that US action is the only barrier to the UNSC action. At that point, it's an FX debate--and depending on who the more solid T debaters are, I think that can go either way.
We all know how fun it is to debate inherency!