The idea that there were fine people "on both sides" has to be interpreted in terms of who the two sides were.
One side was made up entirely of white supremacists and white nationalists. That was the reason they were there -- it was also, one imagines, why they were all happy marching behind people shouting "Jews will not replace us":
https://www.theguardian.com/us-news/2017/aug/16/charlottesvi...
The only reason to say "on both sides" -- and he stressed "on both sides" -- was to create an equivalence between those sides. When there is no equivalence. One side was an organised white nationalist anti-semitic, racist protest, and the other side was a pretty disorganised bunch of people who think things like that are unamerican.
He had one job, to condemn the Unite The Right protest, and he chose words that made it explicitly clear he did not.