Does your logic fuel your emotions, or do your emotions dictate your logic?

When it comes to logic some people claim to let logic fuel it, a logic based on known facts or evidence pointing to an expected conclusion. For example, natural selection of species survival weak or useless members is a drain of resources from the rest of the body. Logically those non-producing elements should be culled from the body. However if the member that happens to be in the non-performing group is a relative, close friend or even an object of affection logic goes out the door and people want to keep that person around even though they are a drain. They let emotion overrun what is basically sound logic. Or someone may be passionate about immigration being the reason for job decline in the US, and that emotion or desire to hold to that belief clouds the logic that many of the jobs that are done by illegal immigrants allow them to buy goods and produce they want at a price that is cheaper. Those types of incidences happen every day, every week in a number of different scenarios. If a person is going to claim being a person of logic and have facts frame that logic, should not they be genuine to the belief even if it seems cruel or heartless? If they are going to let emotions rule, then should not they have the present of mind to go with actual fact or admit they ignore facts as to make their logic more plausible?