As to why spend time refuting the falsehoods of the pre-tribulation rapture, it is three fold
1. It gives people the false idea that they will be magically taken away and not have to suffer for Christ. This weakens them when tribulations DO occur. Christ told us that we would suffer for him.
2. It minimizes the suffering faced and facing Christians outside the USA and at different periods of history. Some p-t rapture folks dismiss them as not good enough to have been magically taken away
3. It is a stick for the non-Christians to wag at us - ever since Miller
Oh you are a Seventh Day Adventist.