the consequences of the sheer stupidity assuming that is what it was and not malice doesn't even bear thinking about. It reminds me of a film from the 80's with someone who had a grudge against motorbikes. You can imagine what happened there.
Someone I know had the same happen. It happened to be when the hunt was going to meet in the area so blamed on hunt sabs. Fortunately she was just walking and saw the wire at neck height.
A few years back a motorcyclist was killed by a wire strung between two trees. Apparently there had been disputes over the right of way (I think it was a footpath or bridleway but motorcyclists had also been using it). I only saw the original report so I can't remember if anyone was arrested.