What else can you trust? It gives you the only truly personal reflection what is and is not right in relation to you and you alone. Everyone else who preaches to you does so from some personal interest, or may do. But your conscience only talks to you. I would listen to it, it is connected to all of your bodily and mental states. Ignoring it has rather painful consequences, and killing it or curtailing it makes you a soulless machine and easy to spot as someone to avoid.