"What I would lik to know is why SOME helicopter pilots think that they can use private strips without any permision?"
I wouldn't do it. I'm sure most heli pilots with any common sense wouldn't do, either. The only answer is to ask the individuals concerned. Why not just find those actually responsible and point out the error of their ways?
Similar question to my own; why do some car and heavy van drivers think it acceptable to park on my private frontage blocking my gate and /or turn round in my driveway, sometimes dislodging paving slabs? Is it because they are rude, inconsiderate, or just downright thick between the ears?