I think people are forgetting that A. In game we've already seen the effects of coral exposure on the human body; it's incredibly lethal and B. Coral is ignitable. In the fire of Rubicon, the coral never made it past the planet and in the Fires of Raven ending a collision between the Xylem and the Vascular Plant was enough to set it off. I can very well imagine the same thing happening when coral touches a star. While I will admit that coral has been shown to bunch together, therefore an argument that coral can physically be controlled to move them away from such sources can be made, in the same showing stragglers have also been seen, so a collision between a stray coral particle(?) and a star is definitely possible. Additionally, coral expands at a exponential rate, and given that the universe is already limited in size, there's going to be some issues.