I agree, people do lie. And some lie a lot. Others lie only when they need to, such as telling a friend that their new hairstyle looks nice when it doesn't. But you are assuming that just because you have developed a desire to have total honesty, that everyone else is going to agree with you. Even if you order a person to be totally honest with you, they can still lie and you will not know it. The key to this is not to see this as a deception against you, but for you to develop a way to respond to people that does not leave you feeling vulnerable to everything they say.
For example, if you ask me do I feel you are a nice person. I can say yes, I do. But you are not sure if I am telling you the truth. What can you do about it? You can believe me, in which case if I am telling you the truth, you and I both are happy. But if I am lying, then you are being deceived. What then? So I don't think you are nice. What happens then? How is your world affected by my belief? Is it so important I tell you the truth that I do not think you are nice? And if I do, what happens? Finally, why is my opinion (truth) so important to you? Who am I in the scheme of things and why do you give me so much power over you?
I think you are assuming here that you will believe everything anyone tells you blindly if they are not forced to be truthful, which is not true. You have suffered a severe trauma and no longer are blind. When someone goes through such an experience, it changes them. They can react in many ways, but in your case, I think it made you aware of how others can be deceiving. Because of this, you will no longer be as easily accepting of a lie or deception. But you are taking it to the extreme in order to protect yourself. Now you are demanding complete honesty from everyone regardless of their motivations or intentions.
You mention the example of drunk driving. As your therapist, it is her goal to make sure you get what you came for, peace of mind and good mental health. Telling you that you were responsible for the death may be true, but is it helpful? You may already know you are at fault. Does her confirmation of that make your feelings real? And if she denies you are at fault, does it make your feelings less validated? The key here is what you feel. You are giving away your power to understand what is true and what is not. It is not other people's ability to tell the truth that is important. It is what you believe.
In the case of your attack, you are saying you feel responsible. But that is not the truth, it is a deception you tell yourself because that is how your mind is coping with it. It is hard to know the truth when you are trying to process so many strong emotions. Forcing your therapist to be honest with you about the attack is a way for you to be sure that you are not deceiving yourself. For if she is honest with you, you can be more sure that you are not responsible for your own attack, making it easier for you to heal.