- Reapers dont have human emotions - they dont care, they dont do vengeance, hold grudge, ...
- Reapers dont use current technology, they have their own, so stealth that works again current technology wont work against theirs, why would it, why would they use sensor technology that can be fooled that easily, not to mention that stealth didnt work against collectors, so why would it work against reapers?
- Reaper IFF is as was said before, just ID of a Dead/Missing reaper, I'm pretty sure that even stupid humans if they suddently hear from dead/missing person get a little suspicious, so imagine what would sentient machines with a hive mind and collective decision making in splits of nanoseconds do?
its the blood magic in front of templars thing all over again ... the lore sounds awesome, but then writing throws all the lore to a trash, because they would have to actually think about how to make awesome scenes to make sense ...