The main reason why harnessing wind energy is good for environment is the fact that the more wind energy we use the less fossil fuels we need. Fossil fuels (oil, coal, and natural gas,) though currently being dominant energy sources, are very dirty fuels that do not only create air pollution but more importantly are directly responsible for the strengthening of climate change impact.
Unlike fossil fuels wind energy doesn't contribute to increase of carbon emissions in the atmosphere and therefore doesn't contribute to climate change. It also causes no air pollution.
Does this mean that wind energy is the perfect energy source when being looked at from the environmental point of view? The answer is no because there is no such thing as perfect energy source, regardless from which perspective you are looking at it.
So how to then determine whether certain energy source is environmentally friendly or not? The best thing to do is to compare it with traditional fossil fuels and then measure the amount of negative environmental effects in order to see which energy source comes on top.
Wind turbines have indeed led to deaths of thousands of birds and baths but this is nothing compared to millions of animals that will disappear if climate change continues to strengthen its impact in years to come. Furthermore, many new wind energy projects are equipped with radars in order to spot birds when approaching so this issue definitely looks to have a potentially easy solution.
Some wind energy opponents also claim that large wind farms have negative visual impact in given environment because it is not easy to integrate them with every landscape. But what's the alternative to this? More coal power plants. Thank you very much but I would much rather look at wind turbines instead.