Tanning Chemicals Bad?

I'm relatively new to tanning hides and have been using a citric acid pickle and either an aluminum sulphate soak or Trubond 1000B paint on. I've had a few conversations lately where the other party has sort of thumbed their nose at "chemical tanning" as being unsafe for people and the environment. Sort of like there's a stigma attached that I don't know much about. The aluminum sulphate is literally made to be poured into the soil for blueberries and azaleas so i can't figure on that having much of an environmental impact. I honestly am not sure what's in Trubond but it's a paint on so I don't have any waste. I usually dump the citric acid pickle on my driveway to kill the weeds, which it does, but I don't see it having any unintended environmental consequences. What am I missing? Both times I had the conversation the other party was more into brain tanning for environmental and health reasons.