Why I HATE LIARS!!!!!!!

In my world things are dealt with rather simply. We kill, eat what we killed and mate that is about it. However, I have human friends, well I use term loosely, and they are so deceitful. I can't understand why they lie about things that do not matter. Others lie about the most important things - ie relationships. Others carry on 2 lives by cheating on their significant others. I don't understand this behavior. Why not just kill the one you are cheating on and then you won't be cheating? That is what we would do in my world. Ultimately, I hate liars not because they lie that is their own shortcoming. No, I hate them because they make me question my sense of judgement and gut feelings. For example, when you know you are being lied to you, you feel it, but you don't say anything and you think "well, maybe it is me". I say when you feel that way "kill them"!