Because he moves between stars on errands that may well take him to the Romulans one day?
As already said, "Balance of Terror" already contains all the elements that make us think Spock wasn't completely candid there. He jumps to amazing conclusions about the aggressiveness of the Romulans, and then presses forth those conclusions with atypical vehemence. He goes completely against his already established minimum-force, gentlemanly approach to hostilities, let alone his later-to-be-established pacifist leanings. The thought that first comes to mind is definitely "old scores to settle"! Also, Spock has a personal stake there, being suspected of treason and sympathies with the enemy. The suspicions do warrant some speculation, IMHO...
Timo Saloniemi
As already said, "Balance of Terror" already contains all the elements that make us think Spock wasn't completely candid there. He jumps to amazing conclusions about the aggressiveness of the Romulans, and then presses forth those conclusions with atypical vehemence. He goes completely against his already established minimum-force, gentlemanly approach to hostilities, let alone his later-to-be-established pacifist leanings. The thought that first comes to mind is definitely "old scores to settle"! Also, Spock has a personal stake there, being suspected of treason and sympathies with the enemy. The suspicions do warrant some speculation, IMHO...
Timo Saloniemi