I have been posting to Christians for a number of years, so I discovered that a long time ago.
It really is all about their emotional attachment to Jesus, so even if I can prove that Baha'u'llah was the return of the Christ Spirit as Baha'is believe, that won't matter because it has to be the same man Jesus, as if they would even recognize Jesus if He came floating down in the clouds as they believe He will.
For Christians it is the attachment to the Jesus that was depicted in the New Testament, the Jesus that dies for them and then allegedly rose from the dead, and it cannot be any other. Unfortunately for them, Jesus said that His work was finished here and He was no more in the world: (John 14:19, John 17:4, John 17:11, John 19:30, John 18:36)
But they never respond when I post these verses because there is no way to respond and still maintain their beliefs.