Earlier quoted context omitted.
"I don't see why you think it's unethical for them to try to poach your partner." This is Arthur Anderson thinking, not Y Combinator thinking. If you jumped on one of my best people "in an instant", then you better be prepared to set aside resources to deal with me. Are you sure you really want to do that?
If Arthur Andersen thinking is defined as "don't take petty crap like this personally, and focus your brain cycles on MSPW", then I have to side with Arthur Andersen. But I suspect that this is a matter on which Paul Graham and David Duncan would be in agreement.
And it certainly isn't petty. I don't care how much technical talent you have, if you're not prepared to compete in business, whatever the threat, you're toast. Poaching my people is crossing the line.
And I don't care what Paul Graham, David Duncan, or anyone else thinks. On this issue, you shouldn't either. Ethics is non-negotiable.