^ well-balanced reply
Let's keep aside the productivity because it wasn't mentioned who specifically is concerned and I think it shouldn't be. let's assume that TBS - as any school - will select reasonably productive people from the start, and the few times that someone really turns out to be a lemon won't trigger anyone to start a thread like this. So it boils down mainly to the fit question.
One point is, how do you actually become a better place? I think that HR policies can actually play a significant role there, making sure the people who come and stay actually have a lasting positive impact sounds like a reasonable approach to me.
The downside is having to sometimes part with some people - and that's even more delicate, because if you overstep then you won't even be able to recruit the people who would make a positive contribution anymore (as you said). What constitutes overstepping always depends on what's customary in a given area, and judging from the original post, it actually sounds like TBS could have overstepped the customs of academia here. In the end, it would be interesting to hear the other side in this story...