Hi Zane,
If Mr. Fisher wants the photo of his Mooney taken down, I would say, go ahead and take it down, it is only one of hundreds you have in your inventory, and it is his loss, not yours because you may have taken a great picture of his plane, that he might have eventually wanted to get a copy of.
That he was upset enough to threaten you with his "legal team" (who will tell him outright that his aircraft is in the open and plain view, and utilizes public property, public airways and is not covered by any legal precident), why go through all of the back and forth headaches, with one irrate individual.
I have had only a couple of such requests, and believe it or not, after the fact, these same folks invited me back to take pictures at a later time, including interior shots of the jets (they were in the middle of business dealings the first time around).
There will be no way to determine the reason for his demands, but the one thing we do have to be careful of is that, one of the rules for posting a picture on Airport-Data, is that it states:
3. You must be authorized to submit the photo.
This protects Ken, and the rest of us from some "potential" problems down the line, so lets not take a chance of losing this valuable real estate just because we know that your are in the right.
Go take some great pictures of another airplane, and I think you will find (as I think Bluedharma has seen while we have been at Centennial Airport taking pictures) is that by taking a couple of photo's out to the folks at the field and giving them away, or sending some via email makes real good friends with a lot of pilots in a hurry (You have to remember, a majority of these folks are "really proud" owners of their planes, and take a lot of satisfaction in knowing that someone would be wanting to take a picture of them and/or their plane) and then you get known and people will give you more latitude than you could ever imagine.
My two cents worth, but it has worked very, Very well for me. ....at least for the last 40+ years.
John L.