We have plenty of evidence they were hostile to ships that posed no threat (i.e. before Aegis weapons appeared). You can argue the use of weapons that are incapable of damaging the Thargoids was justification for the lethal response, but in my view it is akin to fatally shooting someone who attacked you with a water pistol. There is no doubt they drew first blood, provoked or not.
Weapons or not. There is no doubt that a lengthy invasion of their 500m intimacy zone will trigger an attack. Carrying a Thargoid Probe, Scanner or Link also seem to be a fail safe way to get on their wrong side. They don't like to be probed either(funny that).
There is still no evidence that they attack commanders based on their personal history, but I would not discount it. It seems that some of us never experience any hostilities, while others gets attacked without warning.