I don't man to labour the point, but if the Baha'i are working towards unity of all faiths, then it's a shame they declared the core principles of Christianity – Incarnation and Trinity – as heresy. By so doing the Baha'i have alienated the most part of the Christian world.
OK, let's tackle this head on.
I would consider that what you have offered in that statement, is foretold in scriptures. I also offer that It is Christ, who as promised, has returned in the 'Glory of God' the 'Father', that has given Christains this advice.
2 Corinthians 4:6 "For God, who said, “Light shall shine out of darkness,” is the One who has shone in our hearts to give the Light of the knowledge of the glory of God in the face of Christ."
History proves undoubtedly that mankind always rejects and persecutes the Messengers of God.
What else can be offered? A Baha'i offers naught but Love peace and unity under One God, that is what God has asked of us in all past Messages. No one has to change their faith for this to happen, if they choose not to, they just have to practice that Faith.
So, if doctrines prevent Christians, Muslims, or others embracing all God given Faiths, then why is it the Baha'i being blamed? How else will there be one fold with one shepherd? God has given us diversity for a reason.
How is a Christian going to embrace the Quran and the Message of Peace it contains?
In turn, how is Islam going to embrace people of other Faiths?
Is it not now apparent the world needs to again embrace God and Love, not exclusively, but with more understanding of what it is to know and Love God?
Regards Tony