Has it been rigorously shown that it can never be tested? Or is that your prediction?
But yes, not rigorous.
People talk about this as though it's an attempt at deception, whereas two people notionally working in string theory could in fact be proposing highly incompatible models which would be conclusively ruled out (and a lot of them have been in so far as that can be done - i.e. experimentation has put tight bounds on their possible parameters).
Yeah... except that hasn't been proven. That's just your belief, right?
I don't think anyone has proven that string theory can yield no testable predictions. I think if someone had, that'd be a big deal.
And I don't think we should pretend that an open problem is closed just because we don't like it.