I feel kind of uncomfortable going to counseling

[Brian37]

I expressed my anger towards one of my parents mistakes multiple times. My anger has become serious, so I made an appointment for counseling. The problem is, I don't feel comfortable talking about this particular subject to my therapist. 
My parents' mistake has to do with religion, but I don't want counseling for my disagreement with religion. Yeah, religion makes me sometimes angry, but not to the point where I have problems controlling myself. I also don't fear being judged for my atheism on a regular basis. I don't know if my therapist is religious or not, and as much as I complained about religious in the past - including moderates - I won't mind my counselor being religious. All that I want from him is that he does his job right. I don't want to discuss with my therapist whenever religion is good or bad or how to live as an atheist, I just want to discuss with him about the fact that I was brainwashed by fundamentalists for almost a decade right under my parents noses, and when they found out they didn't understand how bad the situation was.
Here in Europe people are usually more indifferent towards other religions and atheism and most christians are moderates. But part of me still fears that my therapist might want to convince me to return to my religion. 
Also, I never talked directly to someone about my parents' mistake. The most I did was writing on this forum where nobody knows my real name. I know that the counselor will keep my secret and I met him before, I highly doubt that he'll judge me, but I still feel very uncomfortable talking to him about this.
What should I do?

You seriously need to get over this fear if you want help. Any ethical professional isn't going to violate that trust. The only time they ethically do that is if you say things that are physical threats to others, or admissions to violence to others. So if you are not threatening anyone with violence you should have nothing to worry about.

If they are pointing you to a religion then you can simply tell them to skip it. If they keep pushing it, then they are not being ethical. 

There are doctors and even psychologists whom hold a religious belief, but do ethically leave it at the door. If they cannot honor your wish to leave religion out of the therapy, then you should find someone else.