Things orbidden have a secret charm.

If you have two clerks, there's more of a temptation to resist, which could cause an escalation of the situation. And if it is a truly heinous act of violence, you just put more people at risk.

dangerous chemistry

My head spins as I glance away, refusing to get sucked back into his gaze when so much is at risk.

Arthur Dent: What happens if I press this button?
Ford Prefect: I wouldn't-
Arthur Dent: Oh.
Ford Prefect: What happened?
Arthur Dent: A sign lit up, saying 'Please do not press this button again.

The last temptation is the greatest treason: to do the right deed for the wrong reason.