i'm suspicious of any group in which there is no self-doubt. it's only through self-doubt that we find ways to improve ourselves. That said, I know what you are saying - there does seem to be a growing sense of unease among many other groups of Judaism, especially as the reform movement becomes increasingly liberal - leaves folks like me in a sort of a limbo.
They're unapologetically devout - that's their prerogative. I know of no antagonistic behavior from that group with respect to outsiders, which I find to be very unusual. I'm naturally skeptical myself, but I can't find fault with them.
I think you misunderstand what the poster said about "self-doubt."
"Hillel said: Do not separate yourself from the community; do not be sure of yourself until the day you die; do not condemn your neighbor until you have stood in his place; do not make a statement which is not readily understood thinking that it will eventually be understood." [Pirke Avot 2:4]
Of course Chabad is about self-improvement and always striving to better oneself. No one is perfect. I know I certainly am not.
I think what the poster meant (correct me if I'm wrong) is that we are more confident in our belief that G-D exists and what our mission is on earth.