Some say that coal is not the only alternative and it can be processed in a safer manner, but this is wishful thinking. Renewable sources involve a costly manufacturing process that is not necessarily green [2] and there is still no good, scalable solution for a cloudy, not-windy day. And don't get me started on hydro power and how we have at best no idea about the long-term environment impact of it. Then add to it the way politics works and that dirty coal works just fine for your common Joe, as long as it's burned elsewhere.
Nuclear power scale well, can be safe when done properly, and if nothing literally explodes is the cleanest option out there. Compare the victims of coal mining accidents alone with those of nuclear disasters [3] - and those do not include the air pollution victims.
[1] http://www.scientificamerican.com/article/coal-ash-is-more-r...
[2] https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emis...
[3] https://en.wikipedia.org/wiki/List_of_accidents_and_disaster...