@bythewell - It's too late now. And there are plenty of positives to the dam. That flooding you mention made the Chinese government take steps to start reforesting the area.
And the amount of air pollution the dam saves is huge. Not only from generating clean hydro electricity, although that's a big part of it. It also allows them to ship a lot of goods by boat rather than by truck which also reduces pollution by a good amount.
There is very little technology in the world that's perfect. Hydropower is no better or worse than anything else, really.