Not that this topic has been beat to death in many prior threads and not that posting here is going to change a single thing but....
Drones are not allowed to be operated in NP for _several_ reasons... harassing wildlife is only one of those reasons. You ask what harassment will take place at 50 or 100 feet? You may not know this but... drones can (and are) flown lower than that. They _only_ way your argument works if they cannot. So obviously your point is.... pointless. It is not like anyone would ever use a drone to harass wildlife, right? When I search on Youtube, this is the 4th entry:
Feel free to jump to the 2:00 mark. From that point on, the person _continues_ to get closer and closer and does not leave the deer alone. Now, I'm not going to waste my time linking to the hundreds of other videos where a drone gets too close to wildlife. The NPS has _1st hand knowledge_ that this was going on. Keep in mind... it is 100% illegal every place in the US... but people _still_ do it. The repercussions are that it seperates young animals from their mothers and those animals cannot fend for themselves. But hey, that person could not do without a drone shot of animals. After all, it is their right to have it.
The other reason why drones are banned from NPS is because of the damage they do. Feel free to Google Yellowstone and drone. I'll simply allow you to educate yourself. Keep in mind... this all happen when there _was_ a ban. Think what would happen if everyone could fly a drone the same way.
Last reason is that the NPS is charged with preserving the park as it is for _everyone_ to _enjoy_. I can think of nothing better than enjoying a great view.... with 20 drones buzzing around. But hey, you need that drone shot. Screw everyone else. It is not like you can fly in millions of other places.
As I mentioned above, this topic has been beat to death. If you don't like the NPS ruling, feel free to contact the appropriate people to have the rule change. As your lawyer friend should have mentioned, in addition to rules being passed because no one objected... rules won't also change if there is no objection.