Okay, I had to do some extra digging. And I was a bit off in my original comment: accept returns a socket only when a connection is fully established, that is,

Okay, I had to do some extra digging. And I was a bit off in my original comment: accept returns a socket only when a connection is fully established, that is, after the ACK from the client. Until then, the application is oblivious to the connection attempt. So sending SYNs by themselves is it too hard on the servers.