Flame in the Streets was adapted from a stage play and often feels like it. The acting is occasionally stilted and other times too heavy-handed. Not the worst offender nor entirely out of step of other performances of its mostly pre-method era. It's just that, given it's serious subject matter, it didn't need any extra help to wind up the audience and it might have done a better overall job if it was more clever and subtle in its approach. Additionally, some of the dialog, especially from minor characters, is very on the nose and almost comically rote. In some ways this film feels more like it's from the 30s or 40s and not the early 60s.
The plot involves a union leader who, full of righteousness, defends a black man's promotion to a minor management role in a manufacturing company. His progressivism and sense of fairness is challenged and turned on its ear when he learns his daughter intends to marry a black man. All of this takes place amid the backdrop of his crumbling marriage and a neighborhood that has started to boil over with racial tensions.
While it's easy to criticize the execution, I appreciated how directly and incisively it goes after its controversial themes, particularly that of the half-way liberal who will righteously advocate for the downtrodden as long as, on some level, he can continue to see them as lower and separate from himself, and those truly close to him. That hypocrisy is still very relevant today as many talk endlessly and fiery about inclusion, but at the end of the day still seem to be surrounded by people who look the same as they do.