Uh...
T'Pol never said anything remotely like, "Visiting P'Jem is forbidden, against everything that is holy, you cannot go there."
Archer is (however grumpily) trying to look at Vulcans in a less prejudicial way, and T'Pol is trying to help him, which might be a reason behind his wanting to see P'Jem and her agreeing. Didn't help that the Vulcans at the monastery were another pack of liars. But I recall Archer being pretty nice to T'Pol while they were down there.
The Vulcans were being held hostage by the Andorians.
Vulcan violated a treaty with Andoria by hiding the listening station on P'Jem.
T'Pol chose to give her scans of the listening station to Shran. Archer didn't hold a gun to her head. She knew Vulcan was in the wrong.
T'Pol never said anything remotely like, "Visiting P'Jem is forbidden, against everything that is holy, you cannot go there."
Archer is (however grumpily) trying to look at Vulcans in a less prejudicial way, and T'Pol is trying to help him, which might be a reason behind his wanting to see P'Jem and her agreeing. Didn't help that the Vulcans at the monastery were another pack of liars. But I recall Archer being pretty nice to T'Pol while they were down there.
The Vulcans were being held hostage by the Andorians.
Vulcan violated a treaty with Andoria by hiding the listening station on P'Jem.
T'Pol chose to give her scans of the listening station to Shran. Archer didn't hold a gun to her head. She knew Vulcan was in the wrong.
But my point-she very firmly and strongly told him that it wasn't advisable to intrude on them, and he pestered her until she relented and made arrangements. Her advice got tossed out the airlock, without condsideration by John-boy. I'm a human from the USA. If I go to Rome and pass by a monastery on a tour, and want to visit, and am told it would be disruptive to the monks routine, I don't get to just barge in because I wanted to.
Putting Earth at risk in the process? 
