The "poor witness to the Gospel" was in this LCMS leader who publically recognized the validity of false religions by participating in a joint religious service in Yankee Stadium. His participation in such spoke against the very words of Jesus when He said. "No one comes to the Father except through Me."
One cannot preach the truth to those who do not believe by only staying inside the church walls of those who already believe.
Did this Bishop actually validate the other religions, or did he simply attend a joint service with them in an effort to heal all he could through the power of Christ?
Christ spent a lot of time with deniers of the faith, heretics, and people who just got things wrong. For us to hole ourselves up and only be in the physical company of those who already believe as we do is to deny the example of Christ, and may well lead to denying Christ altogether. I know you don't promote denying either, of course, I'm merely pointing out what CAN happen as a result.
Now, as for the LCMS "hindering the Gospel" or anything like that, I don't believe it is. I don't believe it's promoting it to the fullest it can, but then no church truly is, in all honesty. Maybe individual congregations are, but as a whole, denominations don't.
In keeping with my "wish for unity" mindset, I refuse to believe the LCMS is trying to harm Christianity, or trying to slow the growth of the faith. I believe their overall practices and seeming mindsets of "Come to us because we won't go to you" (I said seeming, not that it actually is, and there is no doubt it is perceived as such by many, if not most and if not all outside of the denomination to be so) do this, but I cannot and will not believe that it is by actual design of goal.