IT IS ONLY USEFUL against terrorist groups, rogue countries in violation of the UN, and accidents. WHICH OF THESE are YOU supporting???

It's not useful against these people if they have more nuclear armed missiles than we would be able to shoot down, and there's absolutely no guarantee that such would not be the case (although your assertion that terrorists would have any nuclear armed missiles is pretty preposterous, so I think we're only talking about sovereign nations here). So the only effective way to prevent such an attack would be for us to behave in such a way as to promote justice around the world, instead of working so hard to spread injustice, as we are doing now.

And since you keep saying that the US would be obliged to blow up the whole world if even one nuclear armed missile hits us or one of our allies, you are willing to put all of your faith in a system that you yourself have admitted may not be up to the task to try to prevent the destruction of the entire world, instead of doing what is needed to make the world a genuinely safer place.

Since we have established that no one can guarantee that this system can take out all incoming missiles from rogue states or terrorists, and also since our government is actively working to create enemies wherever they possibly can, and where none need exist, there really is no legitimate reason for building such a system, and in fact, there are many very valid national security reasons for not building it.

They are building it for first strike capabilities against countries who have a small number of bombs.

And by the way, we are a rogue country in violation of the UN. I sure hope nobody uses this as an excuse to nuke us