I would say carbon is definitely insurance. In your case, if your sinulara had been in a little bit worse shape, or if you had happened to be on vacation when things went bad, you may not have been so lucky. Plus, I have a feeling that if traumatic damage to soft corals releases lethal levels of toxins to stonies and fish, they are probably releasing some level of toxin at all times. I worry about retarded growth and long term effects. You have to remember the density of coral mass per volume of water we keep in our tanks is unnatural by orders of magnitude. You have to take some precautions to make up for this proximity. Conversely, I haven't seen any evidence of any issues with running carbon, except for the aforementioned issue with tangs and HLLE, and you shouldn't keep tangs in a 65g anyway, so not an issue. I suppose the only possible problem is that it makes the water too clean, especially when combined with aggressive skimming (which may also help with soft coral toxins) but there are products to help with that if you're concerned (reef energy, for example).