I don’t know about the whole debate, but from what I’ve read, the KJV is much more poetic and straightforward, while the new translations are very watered down and often so concerned about direct translation that they are wordy and awkward.
That is not the reason the KJV only people are KJV only. What it has to with is that most of the newer translations come from different sources than the KJV. For example the New Testament of the KJV is mostly translated from the Textus Receptus where as the New Testament of most of the newer translations comes from the Nestle-Aland text. There are various differences between the texts. There are multiple verses that appear in the Textus Receptus, but not in the Nestle-Aland text. It is believed that through the years when people were copying the text years and years ago that the text was added to. The verses that appear in the textus Receptus but not in the Nestle-Aland text are verses that are thought to not have originally been part of the Bible. They were therefore removed. This is why some verses (like Acts 8:37) appear in the KJV but not in most newer translations. KJV onlyists believe the sources used for the new versions are corrupt. They believe that instances like Acts 8:37 are actually attempts to remove things from and change the Word of God. They believe that Satan is behind the newer versions and he created them to keep people away from the real word of God(the KJV). Some KJV onlyists think the Catholic Church is behind the newer versions. Some KJV onlyists really, really, REALLY, hate Catholics. KJV onlyists tend to be conspiracy minded. Some KJV onlyists are downright crazy. Most are nutty in some shape or form. I read and watched on youtube alot of what they have to say. I find there arguments to have huge gaping defects in logic. Just watch a few of this guy’s videos: https://www.youtube.com/user/husky394xp/videos