There was ABSOLUTELY NO COST to kill CoiledCoin. If something has no cost to attack it will be attacked.
Wrong. The cost was luke's reputation (what little was left of it, arguably not a very large cost indeed)
Well that assumes it hurt his reputation much which based on his pool's hashing power it didn't.
It also assumes the attacker is going to make the attack public (which Luke didn't have to do).
In the case of botnet or private farm attack nobody would ever know who executed the attack.