Also consider the speed of light is also the speed of causality. If there was no such limit it means it would be possible for effects to precede causes which would lead to a very different kind of universe!
Actually, it does. Because of relativity events that occur at the same time in one frame of reference do not occur at the same time in another. A delay of zero between two different points implies that there is a reference frame where the delay is negative.
Relativity was derived as a direct consequence of imposing an invariant speed of causality to the Lorentz transformations, therefore it cannot tautologically be used as justification for an invariant speed of causality.
"Imposing an invariant speed of causality to the Lorentz transformations" does not sound quite right. I think it is more like assuming that the Lorentz transformations are the true symmetry of mechanics. If one wants to keep that causal, there cannot be information moving faster than the speed of light because there is a reference frame where said information would be moving backwards in time.