This is a very fine picture. If I was you I would remove the trace of a jet plane. Would it be non ethical?
good question! I tried it and of course it looks better. At this picture I cheated even more and killed an ugly electric pylon which was at the left top of the picture. What is allowed, what is not?
Ha, ha! One pylon more or less, it's not so important. You could also choose another standpoint and it would be gone. But I wouldn't cheat much more than that. You're right, there's no absolute rule.