Back to the original question (as hot as those chix are)
Yes of course windsurfing is dangerous to beach users. But only those beach users who are in the water, and there is not many once it hits 20kn.
Ones who remain in the water are naturally given a wide berth as safety is paramount, and you can always show off quite effectively from 50m away.
Of course if I could make my inside turn only 50cm from the water's edge, whilst waving my sail 20m away and over the heads of those walking on the beach, that would be dangerous.

Alternatively, if I fell off my windsurfer and the sail dragged me along the beach for 100m though sunbathers and kids making sandcastles, that would also be dangerous.

Luckily I windsurf huh!