From the last time I saw it, I did get the feeling that our heroes did believe in the "test" theory, not that it made much difference in their actions - but that the Xindi never did. They had tried and failed, and wanted to try again. And they now knew Plan A didn't work, so they launched several others, including the "Carpenter Street" Plan B and the megaweapon Plan C.
Timo Saloniemi