For those who deny the legitimacy of those concerns,
I suggest they consider the following question:
How would the U.S. had reacted in the 1970s and 1980s if Mexico had expressed a desire to join the Warsaw Pact, and let the WP establish bases, including missile bases, there?
For such missile bases on other NATO nations close to Russia, see:
https://www.nytimes.com/2022/02/16/world/europe/poland-missile-base-russia-ukraine.html
https://foreignpolicy.com/2022/01/12/putin-russia-us-missile-defense-nato-ukraine/