Is there any reason for NATO to exist now? I don't think so, but typically organizations, once born, find reasons to rationalize their immortality. Just like government programs.
Here's a case in point: Ukraine Crisis Reminds Americans Why NATO Should Not Expand
Europe is not part of the US. They are old enough to put on big boy pants. Russia is not scary, just corrupt, obnoxious, and untrustworthy. It's their culture.