I agree with the original poster. I don't see thats its credible and realistic for the Federation to agree to not ever create or investigate a cloaking device.
Surely the Romulans have violated any agreements by their behaviour in several episodes in TNG. Their attempted invasion of Vulcan.
If war broke out between the Federation and Romulus would the Federation still agree to the treaty while their ships were being wiped out by cloaked Romulan ships?
I agree Spock and Kirk behaved badly in 'The Enterprise Incident' but thats the Cold War for you.