It's a typical fault of low level rationalists to consider emotions as "silly". Actually, emotions are useful heuristic feedback mechanisms that can make people act in instrumentally more rational ways. Granted, emotions can surely do the opposite, if people are unable to control problematic emotional impulses. But once you are able to use emotions as sources of information, rather than as direct determinants of your actions, you have a definite advantage over those who don't do that.
The problem of a lack of emotions is that it makes practical decisions almost impossible. The environment in which we have to make decisions is extremely complex and chaotic. People who suffer from reduced levels of emotions find it very hard to make clear decisions. Emotions can accelerate decision making. Cognitive rational thinking is best reserved to really important long-term decisions, making strategies, finding out how to world works, analytical thinking, and so on.
Often, low level rationalists are deluded about not being influenced by emotions. That's in part because they may not be very much aware of their emotions, and about those influencing their reasoning. It's comparatively easy to get trapped in a state of denial and to rationalise the conclusions that emerge from emotional influences, rather than being actually rational.