History should not be made into a science because history cannot be made into a science. It is a good thing for history to become more rigorous and scientific in its approach, but the discipline cannot possibly become a science.
In sciences, experiments can be conducted and facts can be proven. For example, a scientist can hypothesize that dropping a weight on a sheet of glass will break the glass. They can then go and test the theory. When the glass breaks, it is pretty clear that it broke because the weight fell on it.
History doesn't work that way. What if you wanted to prove that the Vietnam War was not necessary? How would you prove that? You can't go back and see what happens if the war does not occur. Alternatively, let's say you want to argue that George Bush's election caused the 9/11 terror attacks. You know that they occurred after he was elected, but you can't (unlike with the sheet of glass) be sure that his election caused the attacks.
So history can never be a science, even if it would be nice if it could.