Once you have the cursor where you need it to be for highlighting the text, you use the '5-way controller' to make the highlighting much easier. If you are already using the 5-way controller, is it possible you're 'tapping' the controller instead of pressing and releasing? You're supposed to be able to simply 'press and release,' which then allows you to move the cursor to the end of the passage you wish to highlight. Simply press and release the 5-way controller once again to finish highlighting the passage. 
There are additional instructions in my first reference for highlighting multiple passages. As you highlight passages, they will be added to the 'My Notes and Marks' section. I referenced a video that lays out these same instructions using a visual aid. I know how frustrating technology can be, especially when it comes to sensitive touch screens. It appears after searching around that there are many misconceptions as to how to use this highlighting feature. There is of course a difference between touching, tapping and pressing and then releasing. Amazon itself explains highlighting on the Kindle by 'pressing and dragging,' but the five way controller keeps you from having to do that, making things much simpler.