"there really is no legitimate reason for building such a system"

False- ANY lives saved would be worth it.



"no one can guarantee that this system can take out all incoming missiles from rogue states or terrorists, "

NO-ONE can guarantee that police can stop ALL criminals- So YOU want us to stop wasting money on police? I though that reducing it would be enough to justify it. Since when has the complete guarantee of anything been required for it to be a better idea than burning babies?



"You saying that there are terrorist groups capable of launching ballistic nuclear tipped missiles against Europe?"

YES. Especially when covertly supplied by nations, such as Hezboallah is by Syria and Iran.