A copy is just that, a copy in the eyes of Google. The copy will be penalized in rankings. Your community won't suddenly leave your website to go to the copycat. There are a million sites that copied Facebook but in the end everybody is on Facebook.
That is true, but if the penalties were severe, you wouldn't have Monster, Trovit, Juju, Indeed, SimplyHired, etc. all reposting the EXACT same job and all ranking nice and high.
Autoblogs work entirely on copied content and do REALLY well for how little work they require to setup.
That's true but it still doesn't hurt your own site IMHO. Copying site would be way below you in rankings (especially since Panda update it seems). Whether it's possible to make an autoblog work is a different matter.