It is possible to disagree with both actions; but it doesn't destroy "but you did it first" defense. The precedent[1] happened and was generally accepted, so unless you want to go the quod licet Iovi, non licet bovi route, it is supposed to be acceptable defense.
The principal way is to reject that defense for all cases, including the first one.
[1] And not just Morales' plane; this happened more often than that. Morales and Snowden were just high profile.
Yeah, the Snowden affaire should have been the impetus for a new convention on civil airspace. It would have been a good chance to also mop up some of the worst abuses post-9/11, and re-commit US and NATO to a respectful and democratic future. Sadly the chance was completely missed, even after the red rage for the leak had somewhat dissipated. And here we are.
The principal way is to reject that defense for all cases, including the first one.
[1] And not just Morales' plane; this happened more often than that. Morales and Snowden were just high profile.