Why do guys are so sure?

I precise that I'm neither creationist nor evolutionist at all, I think both of them should be less pretentious and stubborn, and I know both of them have something interesting to say in a scientific point of view.
I have great respect for scientists and people who say they don't know (about the hot topic "creation/evolution") than someone saying he knows, everyone should have his/her own point of view, and I respect that, but how can you guys say , in such a complex subject that is evolution, that this is our ancestor, or this is...or this.. and so on!! i can't take it because I know one scientist says this, another says that, sometimes they literally disagree, because the evidences are so poor, for instance the newbaby of huanity found in Chad by a frenc and african team, by a lake or something, how do they dare proclame that this is our oldest ancestor whereas we see nothing on this skull says it was an ape or something similar maybe extinct like dinosaurs, or a mere animal, that we don't know.
What do you think guys?
But don't get me wrong I respect what you think and say, but I can't bear when you say statements like if they were th total proof, if we really had real proofs about evolution we won't argue on this forum but the fact is that the so-called proofs are so ridiculous, or it can be another explaination like extincts mammals, but whatever I expect your answers to be harsh or something,
but have a kindda smilin' day!!
Sincerely,
David

Thanks for replying,
I agree with you that religion has nothing to do with public science (it's a matter of faith especially in this domain "The Meaning Of Life") and I am a little bit disappointed by creationists who sometimes don't realize that there are sincere and true scientists who do their best in their respectives fields (I know some creationists are really sincere, but some have lose credibility to me) that's why I respect true scientists no matter what they think and if they have really searched for clues in several realms of life, science, sociology..etc..because everything is linked together in life, that's what I actually think.
Here in France we are taught since our young age that evolution is a fact, with prehistoric people...., but I'm realizing today that I didn't really believe evolution, I still think that it took a lot of times as experiences show, but there can be various explanations, speculations, to all what make the Evolution Theory. Such as for the Fossils.
I think this is such a hot topic we can't realy assert for sure that one thing is at 100% sure.
But I still like to hear about new discoveries, I'm not afraid, if evolution did occur then it did occur, I'm not complicated-minded, but so far there is slight evidences (and I understand people who believe in Evolution, it seems true, it's quite logic after all) but as far as I'm concerned when I was a kid it was more like a Walt Disney movie, if you see what I mean, ok gotta go Folks!
thanx for replying with still kindness,
david