0. The "big politics" of international relations is a zero-sum game between the largest & most powerful countries in the world. If dramatic events of global significance occur, it is only because large/powerful countries participate in those events.
1.	The "shape" of the international community is therefore decided by, created by, and destroyed by these large/powerful countries. They act as they please, to secure their national interests, while small/weak countries act as they are allowed to.
2.	If peace exists, it is only because large/powerful states are either in agreement with each other to maintain peace, or because they are in disagreement, but are compensated/softened by a balance of power (sharing similar levels of influence, similar deterrence capabilities)
3.	If agreement is not found, or if the balance of power is shifted in favor of one large/powerful state (US), at the expense of other large/powerful states (RU/CH): the "shape" of the international community becomes unsupported, therefore unsustainable, and peace becomes fragile
4.	Large/powerful countries don't go to war for "ideological reasons" (democracy, justice). Every state is mainly focused on securing material interests, either at home or abroad. While "ideals" are defended only if they are useful in the process of securing material interests.
5.	NATO is a military alliance that claims collective European defense as its mission. However, NATO's largest and most influential member is a large/powerful state (US). This therefore makes NATO also an extension of the deterrence/influence capabilities of the US.
6.	Any NATO expansion, by the nature of common sense and laws of physics, automatically expands the deterrence/influence capabilities of the US - against the deterrence/influence capabilities of Russia/China.
7.	Large/powerful states do not participate in military alliances unless they have something to gain from doing so. Large/powerful states don't allow to expand their military alliances, unless they see personal benefit in doing so.
8.	A large military alliance, that has the biggest military power in the world as one of its founding members (US), cannot have an "open door policy".
9.	The US will always discriminate between "beneficial" and "unbeneficial" new-joiners, based on geopolitical risks, potential risk scenarios, and cost/benefit calculus risks posed to the US by the membership of said prospective new member.
10.	Therefore the US would deny NATO membership for new-joiners whose participation in the alliance could damage deterrence/influence capabilities of the US.
11.	If the US permits NATO membership for specific new-joiners, it is only because their participation either doesn't damage the deterrence/influence capabilities of the US, or because their participation adds to US capabilities.
12.	The "open door policy" is therefore used as a political narrative to allow the inclusion of "assets" into the military alliance which benefit the US.
13.	Given as global power balance is a zero-sum game, then any "addition" to the US deterrence/influence capabilities is automatically a "deduction" from the deterrence/influence capabilities of other large/powerful states (in this case Russia/China)
14.	Going back to the statement in point  #1  - the zero-sum game of power thus concludes that NATO's expansion by itself is an aggression against the deterrence/influence capabilities of non-NATO large/powerful states.
15.	Going back to the statements in point  #2  and  #3  - any aggression against the deterrence/influence capabilities of large/powerful states by other large/powerful states will result in the destruction of the status quo of the international system, and make peace fragile.
16.	The international system doesn't run on the fuel of "democracy", "freedom", or "justice". These are merely luxuries that are available in a world where large/powerful states are at peace with each other, either through agreement or through a balance of power.
17.	These axioms are the laws of nature - nature of human groups, nature of states, nature of alliance. This nature cannot be changed through institutions, ideologies or treaties. It can only be respected, and worked-around in the interest of maintaining peace.
18.	Anyone who attempts to reject the laws of nature of states, rejects the nature of international relations, and instead gives primacy to ideological reasoning even at the risk of war - will inevitably fail and cause destruction.