[apochromat]

My understanding is FTL effects need not violate causality. It could be a question of bounded input - bounded output (BIBO) stability in a system of FTL effects.

[Physicist]

My understanding is FTL effects need not violate causality.

According to special relativity, if you can send a signal faster than light, you can send a signal backwards in time.

[OBAFGKM]

"My understanding is FTL effects need not violate causality."

The problem comes with relativity. Suppose that an observer determines that event "A" is in some way the "cause" of event "B." If FTL communication is possible, then relativity allows the existence of another observer who sees "B" as occuring in "A's" past, i.e., as the effect having preceded the cause.