With a brother like Gaara, Kankuro had to wear his emotions on his sleeve. In the beginning, it was because Shukaku would scent something he was trying to hide and encourage Gaara to dig it out of him. That painful battle could be ended simply by being emotionally honest, and so after a while Kankuro learned to be blunt.
After Gaara wrestled control from the Ichibi, Kankuro remained blunt in order to give Gaara a sense of stability – that although situations were changing, people weren't, and so Gaara didn't have to be afraid.
When Gaara had lost Shukaku and everyone in the world had almost lost him, Kankuro found himself in the position of being blunter than ever, and explaining everyone else's emotions along with his own. Gaara's lack of intuition when it came to emotions was suddenly revealed, sharply separating the identities of 'Shukaku' and 'Gaara' forever. As a centuries old spirit creature, Shukaku had the ability to just know how someone felt. Gaara, the fifteen-year-old boy, had no such abilities.
Kankuro was sometimes attacked for not being stoic – the old way of the Sand – but he didn't care. He knew that no one understood the stabilizing role he'd assigned himself at Gaara's side, and he didn't expect them to. So in spite of Temari's chastising and Baki's occasional outbursts of annoyance, Kankuro didn't 'correct' his behavior for either of them.
The only person that mattered was Gaara. If his adherence to blunt honesty helped Gaara, then he was acting as properly as he ever needed to.