Correct me if I am wrong by my understanding of those two incidents are:
KL007 was squawking and running with her lights on. After the fall of the wall, the FDR and CVR were finally handed over. It was proven that their deviation was a navigation fault. The pilot had forgotten to switch the INS to NAV. Instead, it continued to follow the magnetic heading. This made it cut into Russian space.
That night, the Russians had been hunting for a US Spy plane that was running in the dark somewhere in the same area. It was intermittently picked up on radar. When the KAL007 flight was picked up on radar, a fighter was sent to intercept it.
The pilot has admitted, in front of a camera, he identified it as the Korean 747, he knew it was a civilian plane. He knew he'd be killing civilians. He never once tried to identify himself to the crew. He just fired at it once ordered to. He also said he would do it again tomorrow if tasked to!
As for the Iran Air A300. If I recall correctly, it was following a completely different departure pattern than all other commercial flights that day. It was not squawking either. It was flying directly toward the US Cruiser which had already been harassed by Iranian F14s earlier in the day. It was also in international waters and sent out several warning, including on civilian frequencies.
Both shoot downs should not have happened. However, they are in different categories.
KAL007 was cold blooded murder.
Iran Air 655 was accidental (Albeit a bit of a setup I feel. It was running without transponder and not listening to radio calls in a WELL KNOWN conflict zone).