With some of the things said by some Baha'is, it doesn't come across like this. It sound more like "We know the truth, because our prophet got the truth from God and wrote it down, so there can be no mistakes. The other religions, except maybe Islam, who knows what the original teachings were? All we have is what people wrote about the prophet and his teachings. Therefore, if it contradicts what Baha'u'llah has said, it is Baha'u'llah that has it right, and those other religion have it wrong.
And some Baha'is sound as if nothing could ever change their minds. They did their investigation and have come to believe the Baha'i Faith is the truth.
So, learning some new things about Baha'i beliefs that might turn up later from some yet to be translated book would affect their belief? Or, learning something new about another religion that didn't fit in with what the Baha'i Faith said about that other religion... that wouldn't get them to reconsider their belief in the truth of the Baha'i Faith?
I think this kind of thing does happen to some people. They weren't "deepened" in the Faith, then learned something that they can't accept. Like maybe Baha'i teachings about no alcohol, no premarital, or extramarital, or homosexual sex. Or they get "witnessed" to by a Christians that convinces them that what the Baha'i Faith said about Christianity isn't true. Like that Jesus didn't rise physically from the dead, or that Jesus is the only way to be saved.
So, when has anyone done enough investigating of the truth to know anything for sure? But that is what most religions expect people to do... to accept fully and completely and never to question or doubt again. That's how lots of Christians come across, but so do Baha'is. It's a done deal. Whatever Baha'u'llah has said, and whatever the Baha'i Faith teaches, that is the truth. If they say God is real and Baha'u'llah was sent by God, then, no matter what anyone says or thinks, is wrong. And they, somehow and someway, are mistaken. And they must be shown what is the truth.
And that's what Baha'is sound like. As sure and absolutely positive as a JW or any Fundamental Christian. And coming from that position is not coming with love and humiliating... or coming as a friend who cares about you and respects your beliefs. It feels as though the Baha'i' is coming to convince and convert. And it doesn't help to know that the Baha'i Faith expects their people to go out and "teach" the word. So, most of us are already suspicious if a Baha'i comes on too friendly and is too interested in us. Because we know what's coming. "Oh, by the way, have you ever heard of Baha'u'llah?" "Why no, who was he"? "So glad you asked. Let me tell you all about him."