It didn't need the Kyoto Agreement. The USA had already bound itself not to build this weapons system.

"Maybe the US should just ignore it's treaty obligations"

In 1972 President Nixon signed the Anti-Ballistic_Missile Treaty which outlawed these missiles. Thirty years later President Bush's administration gave notice of repudiating the treaty, and a few months later did so unilaterally.

These weapons aren't there to defend anyone, They are there to provide   defence contracts to friends and supporters. And in fact far from reducing the danger of a nuclear attack they increase the possibility danger of nuclear war.