The value in having Lithuania and Montenegro and not that we need or want their troops to defend us. The value to US interests is in having as many friendly partners who depend on us as possible. Adept use of "soft power" through things like NATO, foreign aid, etc is hugely beneficial to US foreign policy (something that easily pays back the relatively paltry sums we spend) and is one of the major reasons we have historically succeeded in spreading our influence around the world. Kicking countries out of NATO, on the other hand, will (1) turn happy partners into disgruntled non-partners at best (and ultimately enemies at worst), and (2) send those countries elsewhere to look for partners, protectors, and friendly relationships. It is a really bad, self-defeating idea. Even when leaving aside the strategic implications - that these countries are strategically located next to Russia, one of the major potential foreign antagonists with the possibility to start a global conflagration.