The "Middle Ground" logical fallacy is claiming that a compromise, or middle point, between two extremes must be the truth.
Much of the time the truth does indeed lie between two extreme points, but this can bias our thinking: sometimes a thing is simply untrue and a compromise of it is also untrue. Half way between truth and a lie, is still a lie.
Example: Holly said that vaccinations caused autism in children, but her scientifically well-read friend Caleb said that this claim had been debunked and proven false. Their friend Alice offered a compromise that vaccinations must cause some autism, just not all autism.
Example: John Kelly, White House Chief of Staff, says that the US Civil War was prompted by an inability to compromise. He says that both sides acted in good faith. That is only true if you buy the argument that slavery is ok.