Aside from the fact that your link doesn't work, it is not the case that the "United States" collectively said "no, your reason isn't good enough" or some other such nonsense. The United States is a composite of many and thus cannot collectively say anything. Majorities of physical persons within it can say things and sometimes invoke its name on their behalf, but that doesn't make them the collective whole any more than flapping your arms will make you fly.
So who really said "no your reason isn't good enough" then? Abe Lincoln and his faction in the government. And why did they say it? Not because they wanted to abolish slavery. Not even because they wanted to "preserve the union." They said it because they wanted to collect the taxes.