Would you say it or keep quiet to avoid hurting people's feelings? What if the people in question is family, and speaking your mind would cause alienation, though keeping quiet also causes alienation due to a lack of communication? What if it's about the way they live their life but it's nothing that is life-threatening? What if their attitude makes you feel repulsive being around them? That even if they are happy/friendly/jovial towards you you have nothing but ill feeling towards them and can't even make small talk conversation because you just have negative things about them to say?
Go.
Go.