Greg Cox wrote:
One can argue that the Romulans violated the Neutral Zone first, back in "Balance of Terror," destroying several Starfleet outposts and killing numerous Federation citizens. And how was the Federation to know that the Romulans hadn't worked the kinks out of the cloaking device since. Again, was Starfleet supposed to just sit back and hope for the best?
To their credit, Starfleet showed great restraint by not retaliating immediately after the attacks in "Balance of Terror." Slipping past the Neutral Zone to steal some dangerous new technology from a known threat strikes me as a relatively measured and prudent response. And don't forget, this was back in the sixties when spy stories were the rage.
"Mission: Impossible" used to do this sort of thing every week!
You make some good points about the events of BoT. McCoy seemed to think the Romulans were trying to draw the Enterprise into the Neutral Zone to give them an excuse to attack. So, between that and the other Fed members probably saying 'Romulus isn't OUR enemy!'...I think a military response was off the table. So I think you're right about the events of Enterprise Incident being a reasonable response. They also got bonus intelligence in confirming that the Romulans had Klingon technology.
From the Romulans perspective, (In Balance of Terror) their 'finest flagship' just never came back from its mission. Which gave them the answer they wanted as to whether or not the Federation (or Earth, if they don't know about the Feds) was ripe for attack.
And fwiw, the Feds DID know that the Romulans had a new cloaking device.