Agreed. What linked-in does is absolutely the correct behavior. When someone uses linked-in to send me an email, my response should go directly to the user. This takes Linked-in out of the loop of the conversation, which is perfect.

Other networks (I'm looking at you, Facebook), instead trap you in using their interfaces to communicate with someone.

I think Linked-in is actually really protecting privacy in this respect.

Also, if the user grants you permission, you can see their email address within linked-in and avoid sending any communication through linked-in itself.