Geez.
Final word: tetras are FINE with rainbowfish. Rainbowfish are not "semi-aggressive" in the true sense of the word. Like any other fish, they WILL attack and kill a fish that is sick or weak or one they perceive as being thus. Ie: a bubble eye goldfish might as well have a target on it's head for *any* larger fish and some small ones. Fish ain't stupid. They know those eyes aren't normal. Off, off with dem eyes!
I would not, however, put tetras with rainbowfish myself, unless I had a REALLY big tank. They are both schoolers and will get in the way of each other. The tetras will probably end up hiding or staying in the layer between the middle and the bottom.
Again, as a few people already said, rainbows are fine with tetras. Celebes Rainbowfish (which are Silversides, not true Rainbowfish. Sorry hadda get that in there) are one of the gentlest ones out there, just as Leopardess said.
Roan