We thought much the same when we introduced the automobile. Plastic for packaging purposes. Freon to help with the Carnot cycle in refrigerators. These things don't matter when you do them once or twice. But when you start doing them on an industrial scale it changes the equation from 'no effect' to 'unknown effect'. And unknown effect might be anything from negligible to planet wide catastrophe. It would be nice to know where we land before taking off.

Oceans warming up is a big thing, and local effects can be substantial even if global average change is negligible.