Inconsequential? Then you haven't been paying attention to history. We've had freakin huge impacts on our ecosystem throughout our history, even predating recorded history. The disappearance of huge tracts of North American forest. The same for British and European forests. The Colorado River dwindling into nothing. Virtual eradication of Bison. Eradication of the Passenger pigeon. Aborigines causing the unintentional desertification of much of Australia. The current desertification of Africa. Virtual disappearance of Salmon from the North American west coast. None of these have been inconsequential. Some have caused tremendous benefits to people, but all have had significant negative impact.

The result is never clear beforehand — that's the whole idea behind experimentation and the scientific method. Otherwise you're left with fearmongering and superstition.

Many scientists refrain from experimenting on their own bodies. This has nothing to do with "fearmongering and superstition." When scientists do experiment on themselves, they are generally certain that it won't have permanent consequences. Again, nothing to do with "fearmongering and superstition." You categorically state that we won't know what happens.