Fundamentalism of any stripe is a big problem for me. HumanistHeart mentioned the Abrahamic religions, Christianity, Judaism, and Islam. I don't think these religions should be abolished completely -- there is much in value of them, especially when looking at how they evolved through time, and how they have at different times been progressive, or regressed to a more primitive or immoral form, and so forth. However, I do think that as a whole, they must be reformed -- too often are they behind the times rather than ahead of the times. However, I don't particularly dislike them.
There are certain groups I dislike: Scientology (I just watched a video on that last night -- I will be studying it in my Sociology of Religion Course), Jehovah's Witnesses because the beliefs of parents regarding blood transfusions can be harmful, Christian Scientists (in which practitioners have sometimes let their children die or otherwise suffer neglect), and Pentecostalism.
I was exposed to Pentecostalism at a young age, and it is still traumatic for me to this day. Sometimes memories intrude upon my consciousness unexpectedly and I find myself wincing, sometimes gasping in pain or experience a very deep grief and shame. Thought-stopping techniques were used on us, fear of God, fear of hell, fear of the devil. We were manipulated emotionally by music, encouraged to lose control, convulse, speak in "tongues," exorcisms were practiced, and the people in general were very condemning and spread lots of lies about innocent people. When a younger pastor took over, it seemed that things would be more progressive, but the current minister's wife claims to have prayed a friend of mine out of the town. This friend no longer believes, but is still compelled by her husband to attend a Pente church even though he doesn't attend himself, even though she no longer believes. This person also claimed that her prayers caused a family member of mine to develop cancer. For anyone who believes this woman, they put the control of their lives into her hands because of fear.
The way I was taught as a child was that all other Christians are heretical and destined for hell. The length of our sleeves was regulated, our clothing, no TV, etc., and of course the pastors often did the very things they condemned in their members. I witnessed them pull a disabled woman from a wheelchair, hold her up, take pictures, put her back into her chair, and later used the pictures as "evience" that she was healed. This woman has some sort of mental disability and cannot understand the significance of what happened to her. If people were sick, it was often said that it was because of sin or that they didn't have enough faith to be healed.
One distinctive feature of this group is that they hardly ever talked about love and kindness toward others, but if you leave the church (as I did) or don't know anything about it, and especially if you are suffering from emotional problems (as I did at another point in time), people surround you, telling you they love you, you need to open up, tell them your problems. Of course I refused, but I was surrounded by people love bombing me, trying to manipulate me into telling them things that weren't any of their business. And at another point, I was physically trapped in the building by a bunch of screaming people who sent me into a nervous wreck.
I have visited some other Pentecostal or charismatic-leaning churches that aren't so rigid, but I recognized that they employed many of the same techniques, especially psychological manipulation. I can't see anything redeemable in this movement at all and think it would be better if it goes out of existence or evolves into something else altogether, and based on my experience, I don't think it is likely to evolve into something more positive.