Yup...You and the rest of the Chinese boys here definitively do not know what the hell you are yakking about...
First...This has more to do with philosophies than with the technical details of missile interception, although the technicalities of the subject are relevant.
Never mind the clutter of the example above. The important thing to remember -- that for each phase of a missile's ballistic flight it require an increasing technical, financial, political, and militarily capable country to reach that phase.
And...Whenever I see someone bring in MARV, MIRV, and assorted acronyms, I know the person is just trying to hide his ignorance behind the alphabets.
Anyway...The sooner into a missile's flight that you want to effect an interception, and that is the desirable goal, the closer you must get to the launch point. The closer you want to get to launch point, the more capable your military must be. You cannot have such a capable military unless you have a sufficiently strong economy to support that military.
To date, the only country that can station itself near a potential adversary's ICBM launch point -- and please do not bring in multiple launch points as this is only a simplified example -- is the US. We can station a very strong threat/deterrence like an aircraft carrier group off the coast of any country in the world. Believe it or not, we can launch an air attack, from verbal order to catapult action, quicker and faster than the same can be said for an ICBM launch.
If a country cannot have that kind of global reach, then the next best thing is to intercept a missile at the mid-course segment. Financially speaking, very few country can reach this phase. Not only does it require an orbital vehicle, the mid-course segment require long term sensors and this pretty much mean satellites. Another high finance factor that prevent most country from achieving mid-course ICBM defense.
Finally...The last line of defense is the 'terminal' segment. This is where the enemy's weapon is closest to home soil and is most uncomfortable for all. But this is also the most financially affordable defense segment for
ALL countries. It does not matter if the defense is bought or indigenously developed. As long as the 'terminal' segment defense is capable enough and can be fielded, it is affordable.
The 'terminal' segment defense does not require the country to station itself off the enemy's borders, land or sea. It only require the country to be vigilant, as in very capable sensors looking up as high and as far towards the horizon as possible. This is also much more financially affordable than having orbital satellites, EM monitoring stations, aircraft carrier battle groups, and/or repeated aerial reconnaissance near the enemy's borders.
It is not that difficult to envision the finances of each segments and of all summed up. But I do expect a few to totally miss the point...
...completely and throw up those acronyms.
So realistically speaking...Since not all countries can afford the defense segments like the US -- not even China or Russia -- what constitute an effective and enviable ICBM defense should be the 'terminal' segment. If the country cannot afford rotating aircraft carrier battle groups to deter an enemy by being off his coast, then the financial of one aircraft carrier battle group should be allocated towards the 'terminal' segment defense and make that defense as high an altitude as possible.
If the country can afford two or three aircraft carrier battle groups, then a choice exist: Either field a rotating deterrence off the enemy's coast. Or expand that ICBM defense into the mid-course defense segment. If the country is wealthy like the US, then allocate resources towards all segments.
This is why criticizing that 15km interception altitude is being simple minded. Even for US, we do not take that capability lightly and we are financially capable enough to be working on all three segments. Any country that is technologically sophisticated and financially capable enough to develop a terminal segment defense that is kms over home soil is one to be respected. We do so respected.
