But if you're gonna play Time Police and go back to undo the attack on the Kelvin (thus changing countless lives) why stop there? Seven million humans died when the Xindi attacked Earth. Proven tampering from the future. Let's undo that. What about that entire colony killed in ENT: "Shockwave"?
Many big historical Trek events are rife with tampering from future aliens. Some had halfway hack-job fixes (the Xindi attack left seven million humans dead that shouldn't be, many were killed in the First Contact Borg attack, microchips are supposedly the result of a timeship from the future that crashed in the 60's) Yet much damage was left unfixed. Same thing in STXI.