This has been my entire co-op experience in the beta. People rushing through the content so fast Diablo's head would be spinning. Players join games without speaking, and will not respond when spoken to. Its at the point where some players run past monsters to reach the end quest faster....
Why are people doing this?
Doesn't seem like a great way to test the game.
For example, I wanted to test and see if the player revive mechanic actually worked. Ended up having to join 8 different games, before someone would even respond to my messages about trading deaths and testing it out.