There are obvious dangers of thinking you have X amount of fuel and next day taking off with X - ?
I know a Seneca probably cannot carry 6 people in this way, but surely one should never fly without a visual check on the fuel level?
Where I am based there were reports of fuel theft some 10 years ago, but one could never be quite sure, on the school planes, whether it was theft, or whether somebody did a flight they did not put in the tech log. I certainly found (on a preflight) a few cases of fuel being way below the tech log figure during my PPL training.
In fact I am suprised that vandalism in general, around unsecured strips, isn't
far bigger than it appears to be. I suspect the people that do it tend to not venure too far away from their nearest kebab joint, and the mysterious thing called "countryside" is a bit below their radar. Just as well.