I would offer any valid intellectual reason one sees they have to refute Baha'u'llah, would likewise refute all Messengers and also refute God.
The reason is all the Messengers are One with God, as they One and All radiate the same given Holy Spirit.
In the Kitab-i-iqan Baha'u'llah explains how with each new Revelation of God, the "Return" is made manifest and at the same time the same rejections used since time began, are also made manifest.
The God given Messages are spread mostly by the rejection, what a quandary indeed! That is how the Baha'i Faith got to Akka and Haifa.
As well as Baghdad, Constantinople and Adrianople, they all had a Messenger live amongst them, yet most recognised Him not!
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Micah 7:12
New International Version
In that day people will come to you from Assyria and the cities of Egypt, even from Egypt to the Euphrates and from sea to sea and from mountain to mountain.
King James Bible
In that day
also he shall come even to thee from Assyria, and
from the fortified cities, and from the fortress even to the river, and from sea to sea, and
from mountain to mountain
What an excellent prophecy that was!
And this,
Isaiah 35:2
King James Bible
It shall blossom abundantly, and rejoice even with joy and singing: the glory of Lebanon shall be given unto it, the excellency of Carmel and Sharon, they shall see the glory of the LORD,
and the excellency of our God.
Regards Tony