I will disclose somewhat more complicated point by means of analogy. Many citizens of Latin America states have some degree of Amerophobia because of complicated relationships between the United States and countries whither the Monroe doctrine in its various incarnations was applied, and for other reasons. USA destabilized and overthrowed quite a few governments there, not shunning open invasions (for example, in Panama or Grenada; see also history of South American juntas and Operation Condor).

I think we all can agree that countries in Latam region have natural and inviolable right to choose their own (manifest) destiny. ;)

However I suspect that any attempt of Mexican, Nicaraguan, or Guatemalan authorities to join CSTO will meet a very quick reaction from the Stateside, and not especially pleasant one. It even may transpire that said reaction will closely resemble policies invoked by Russia against Ukraine.