You're looking at it completely wrong!
Tobirama knew that the Uchiha were unstable and that they would eventually defect, especially with Hashirama out of the picture. Which they were planning. That's why he gave them such an important role in Village. To give them trust to earn his trust. Trust is earned, not given.
He did he brothers wishes and kept them as part of the village.
Tobirama may see things in a more cautious way then Hashriama, but he still strives for peace.