Why would they trust the Uchiha? The Uchiha were all predisposed to be emotional basket cases anyway, and, Tobirama gave them a job head be good at to try and give their negative qualities positive expressions.
Edit: Let's see, first off, most of the villains have been Uchiha, but, if you need a count down, Sasuke, Madara, Obito, Indra, Fugaku (depending on your point of view), and basically those involved in the coup (again, according to your point of view). They were even predisposed towards hatred and madness.