I feel I have listened to you but that you have not listened to me, since many of your points have been repeated in each post without you addressing my already-raised objections. I begin to suspect (just suspect) that you have some developmental problem like low-grade austism that prevents you from holding this debate properly. Still, I will raise my objections one more time.
You are assuming greater than infinite energy AND time travel to even put it forward as an argument...
No, I am not (and neither is my source). The misunderstanding is yours. I (and my source) made no assumptions whatsoever about how tachyons might form. As I said before maybe they've always existed, or maybe some change to special relativity won't alter the relativity of simultaneity in an essential way while also allowing the creation of tachyons from sub-light-speed matter.
As you approach the speed of light, energy input must approach infinity. To cross it requires a greater than infinite amount of energy. This is impossible, both in theory and practice.
I agree with you here, but yet again your statement is irrelevant. I do not care how one might create tachyons, I merely assumed their existence. I would like to remind you that my original FTL travel discussion was in the context of new discoveries allowing FTL communication, so the existence of a tachyon isn't even my own assumption, but rather my interpretation of someone else's probable argument. My original point was that FTL communication would result in such a radical violation of well-tested principles of special relativity as to be astonishing.
He was aware that infinite + 1 does not really exist, you are apparently not.
You have finally begun insulting me. I insulted you in my first reply and for that I apologize; I was too angered by the combination of your misconceptions and complete self-certainty. I was better in my second reply. I am actually a mathematician, so I probably know many more ways than you for "infinity + 1" to be interpreted reasonably. None of them are relevant here though.
Relativity therefore prohibits producing a tachyon.
Your argument merely shows the impossibility for relativity to produce a tachyon by accelerating a mass from sub-light speeds to FTL speeds. Barring just one method of production does not bar them all, and I've given two other methods above (twice now; you ignored them the first time so I've repeated them).
The theory prohibits this, and relativity has no appropriate application in an FTL scenario (this is WHY you get a causality violation.)
You have it backwards. You do not get a causality violation in an FTL special relativity scenario because relativity has "no appropriate application" there. Special relativity has "no appropriate application" to an FTL scenario because you get a causality violation (and most people want to keep causality). Your implication is backwards, and this is a fundamental error.
The observation in half of the relativistic light cone will be that effect preceded cause (the missile destroys the ship before it is launched.)
This doesn't make sense. A light cone is not a collection of frames of reference but rather the set of points in spacetime with zero interval from a given point. You probably meant to say that in "half" of all reference frames (specifically, those where the velocity along the line connecting the missle's start and end points is in the direction pointing from the start to the end point) the missile destroys the ship before it is launched.
So what happens?
1) Causality violation means that side B can fire their own FTL missile, destroy the ship on side A that launched the first one, and "undestroy" the one on side B by changing the past.
2) Causality remaining intact means that while side B can fire their own FTL missile and destroy the side A ship, the side B ship will remain destroyed, as this event has already happened.
Your argument is again backwards. You assume contradictions in both cases without realizing it--in case (1), causality violation is itself the contradiction, and it immediately leads to the paradox that ship B is both destroyed and not; in case (2), causality remaining intact contradicts the prediction of special relativity that causality is violated. Your contradictory and hopelessly vague discussion of "undestroy"ing a ship and one "remain[ing] destroyed" are artifacts of these backwards arguments.
The information on the cause is relativistic, the information on the effect is not. You cannot use relativity to determine cause and effect here, but cause still came before effect.
I cannot make this make any sense. I am essentially certain it is incoherent.
Unless you being responding to my actual points, I will not reply again.