Wow, that is some bad title. I would say concerns are justified if Russia can just keep annexing chunks from other countries. It started with Georgia and Ukraine and we can see the same events happening in Moldova currently.

Also if Russia were to share a proper border with Poland then that's pretty much guaranteed WW3, Poland hates Russia with a passion.

...I'm sure Ukraine would gladly put down their arms and watch Russia fight eastern European countries instead, if they really want to make this their fight instead of Ukraine's.