The world is full of chemicals right now. One day, humanity will look back at the last 100 years (and probably the next 50) and wonder what we were thinking.
That is still an overly broad category to be worried about in general... just because something is synthetic doesn't mean it is more or less dangerous than a non-synthetic thing.
Non-naturally occurring chemicals, or at least chemicals that we weren't traditionally exposed to in great abundance. Like laundry detergent and conventional shampoo. Those are probably terrible for the environment. When we ban one, companies just create another one.