Actually they are hyper emotional by nature, which has given them a lot of grief (in the form of brutal violence and wars against each other) over the millennia until one guy came up with their philosophy of pragmatic rationality, which as its core element asks vulcans to learn to ritually suppress their emotions.
It isnt so much them considering emotions as useless, more them being very wary of them due to their past, and their philosophy/belief system teaching and emphasizing rational thought as paramount and the highest ideal, and (their) emotions being fundamentally irrational. So they are often a bit miffed when humans for example make obviously emotional decisions.