As an ex biker I'm inclined to agree with you,
There are some dodgy ones about, I was driving up from the West Country a good few years back and a biker pulled alongside and his pillion was trying to get stuff off the boot-lid rack (MGB) I changed speed a couple of times, they kept trying, so I pulled out a bit sharpish, they swung right to avoid me and went into a field at a rate of knots, never saw them again!