Do you want Aztlan separatists getting Russian training arms and training? Before we start playing in their front yard, we had better be mindful of our own.
Ukrainians defending their own country are of course not the same thing as Aztlan separatists invading our country and then breaking away from it.
Ironically, more similar to your example are a minority of Russians in E. Ukraine being supported by Russians against the will of the majority, trying to break away from Ukraine.