i agree with this change, it makes the game more realistic, esp. that patroling planes even during peace reduce moral and can damage buildings.
Can you cite even one instance in 20th Century history when one nation went to war with another over espionage in general, or aerial reconnaissance in particular? In fact, going to war over aerial reconnaissance is almost unheard of. Spy planes may occasionally get shot down, diplomatic protests may be made, but aerial photo-recon is conducted by the major powers every day of the week in 2017. In 1939-40, heck, only one country had a rudimentary early warning radar system, and it could not remotely distinguish between a small civilian airplane and a photo recon plane. In peace time in 1939, the likelihood of a small plane even being noticed was extremely low.
Leaving the decision to automatically declare war in the hands of the game software is the least realistic resolution of all. If the problem is that patrolling aircraft cause damage even during peace, it seems that is the problem that needs to be fixed, not taking the decision to declare war away from the players. Personally, I think this "fix" is far worse than the "problem."