The reason why people trust KJV only is because they are unaware of other translations that come from the same source as the KJV, like the Webster Translation, Young's Literal Translation and about 6 other translations. None of the modern translations derived from the Minority Text contains the entire Word, in fact they come up very short in Scripture because of the omissions.
You can check 1 passage to determine from what source it came. If 1Jn 5:7 is omitted it's from the Minority Text (which has only 3 manuscripts, compared to thousands in the Majority Text), which is the briefed Text, missing much Scripture. The KJV translators were brilliant to employ italicization to let the reader know that it wasn't in the manuscript, but they add words to make the reading correct; and it lets us realize that they were not adding to the Word.
A good example of italicization is that 2Sam 21:19 passage. the phrase "the brother of" wasn't in the manuscript so they italicized it, to concur with the reiteration in 2Chron 20:5, which has no italics. If we look at 1Jn 5:7 it isn't in italics because the KJV translators saw enough manuscript evidence to include it.
You can check 1 passage to determine from what source it came. If 1Jn 5:7 is omitted it's from the Minority Text (which has only 3 manuscripts, compared to thousands in the Majority Text), which is the briefed Text, missing much Scripture. The KJV translators were brilliant to employ italicization to let the reader know that it wasn't in the manuscript, but they add words to make the reading correct; and it lets us realize that they were not adding to the Word.
A good example of italicization is that 2Sam 21:19 passage. the phrase "the brother of" wasn't in the manuscript so they italicized it, to concur with the reiteration in 2Chron 20:5, which has no italics. If we look at 1Jn 5:7 it isn't in italics because the KJV translators saw enough manuscript evidence to include it.
In fact there are already many, many, MANY threads in that forum about this very topic.
In fact the things you just said have been said over and over and over and over in many of those threads.