Vulnerable to criticism? Are you kidding me? Ever go to a JW chat room or visit a xtian site that discusses JWs? One of the first things criticizing JWs is their claim to be "prophets."
I would recommend you purchase Greg Stafford's book, "Defending JWs" and read what he has to say about propheteering as it applies to JWs.
As far as biblical support, well, most Bible prophets were wrong, or they misbehaved, or did something along the way to incur the wrath of the Almighty. JWs feel that they are no different. Of course, it appears to me that both the JWs and the Bible prophets were all basically just plain silly.
And, Naeblis, I will take you up on your offer some time when borders aren't so clogged up with security. Imagine if I told the border officer that I was going to Toronto to get really drunk with some dude I met on the internet.