Working his network to help get a startup's first few customers at large, brand name companies? I'd hardly call that unproductive. In fact, if they iterate product dev on one of these customers, find that perfect product market fit, and scale; well, I'd say he played a roll in their success.
"Perhaps there were issues the OP is completely unaware of?"
The issue is the manner in which the OP was terminated. The company could be totally justified letting him go, just not in the manner in which they did it.
"you can be terminated for any reason... Does that make it "right"? Well, that's a perspective thing."
One, you can't be terminated for any reason.
Two, we are seeing the perspective of public opinion and unfortunately it is reflecting negatively on YC since people don't have a more specific target. Everyone has a 'right' to choose who they work for.
Three, getting terminated is a little more than just perspective. It is an event which can have significant repercussions for a person: mortgage payments, kid's school costs, etc.