i think an alien race would understand war is a part of every society and would understand that we, being a race still young in age, would discover alot of its innovations through military funding. im sure the spaceships they arrive in were originally/ if not still created for militaristic uses foremost and then colonization/ exploration purposes as a secondary task
if i were the ambassador for the human race i would just give them total access to our entire history, if they were truly and intelligent race they would understand our history as being one of violence and justice and any intelligent race would then understand where were are in our history and either leave is alone until we "grow up", which would be fine, or they would try and set us on the right path, which would be even better. if the alien race was set on destroying us then no ambassador could stop them and if our history was the deciding factor then they could pick up on it by intercepting radio waves or tapping into the internet
my basic idea when it comes to aliens is that if they advanced enough to reach us then they are advanced enough to watch us without our knowledge and judge for themselves what the human race is. from that knowledge they can either kill us, leave us alone, or talk to us; either way we have no control over the decision and very little ability to stop them from their ambitions