I know of few courts that condemn people to death on the basis of circumstantial evidence. Even where eyewitness testimony is involved, it is not unheard of for people to conspire in telling a lie. Courts are not foolproof. Neither is science. I know of many people who are fooled by the evidence. Most people today still say the sun rises and sets because, on the face of it, that is exactly what happens.
The tentative nature of the theory of evolution requires that, in order to be honest, its proponents present it in tentative terms, just as do the proponents of intelligent design.
Circumstantial evidence is more trustworthy than eyewitness testimony, and your generalizations aside, people are frequently convicted on circumstantial evidence.