Did Path destroy itself with questionable ethics[1] or is there really no way to compete with Facebook anymore?
[1] http://techcrunch.com/2012/02/07/path-uploads-your-iphones-a...
[1] http://techcrunch.com/2012/02/07/path-uploads-your-iphones-a...
Then they started spamming people in your phone book, completely ruining the entire point of their original pitch. Now they seem to make money selling stickers? I'm not sure why any self-respective developer would still be working there.
I also don't think Facebook's position is unchallengeable. After all, Facebook wasn't the first social network, and it looks like the youth today aren't using Facebook nearly as much as older generations, preferring newer apps like Snapchat.
In all likelihood Path destroyed itself by being a not-very-good Facebook competitor. This says little about the feasibility of toppling Facebook.