I think the basis of most veganism is they can't hear plants scream so they're not squeamish about it. But plants do communicate their trauma, they release gasses when they're injured that tell the other plants (other species, even) "watch the fuck out something is trying to kill me over here" so the surrounding plants can set up defenses. The gasses are also a cry for help to the predatory insects to come and eat the bitches that are nibbling on me. They also release different gaseous "screams" when attacked by different kinds of herbivores (for examples ones that bite off chunks of leaf vs ones that stab and suck). And that's just the aboveground stuff, not any kind of communication that can be happening along the fungal network entwined in their roots. So if there's a chance fungi have a nervous system, there's a chance that the superorganism including the plants connected to them also share that nervous system.