To be honest….

I just don’t get that phrase.  Yet, I hear it or read it, frequently.  What, the speaker’s been lying all the time til now? And I should trust what he says??  That phrase just puts my hackles up.  I think I understand why they say it – they want to emphasize what follows and make sure the reader or listener notes the truth of the statement, but I contend it shouldn’t be necessary in the first place.  For the life of me, though, I can’t come up with a replacement phrase.  Thoughts?