People don't always want or need to hear the truth. That's the risk you run when you tell what you perceive as the truth. An old test is to ask: Is it true? Is it kind? Is it necessary? ... Only say it if the answer to two of those questions is "yes"
They're probably not mad about your being honest. They're likely mad about what you did. For instance, you can't honestly tell someone that you burned down his house and wrecked his car without him getting upset.
Maybe they are just in denial and aren't mentally prepared or accepting to hear your opinion. Also, everyone's perception of truth is different. Maybe what they believe is the truth in their opinion, and you what you believe is true in your opinion. Maybe one of you is correct, maybe neither, depending on how much knowledge and facts you have been exposed to on the particular subject. In some cases, a majority rules approach could be best, sometimes not.