Actually, that's a generalized problem with firing protections of any kind; the harder you make it to fire anyone, the less likely they are to be hired in the first place. Another case where second-order effects can end up dominating the end results. "At-will employment" sounds like a worker disaster if you only consider first-order effects, but in my opinion it is actually the preferable scenario for a worker if you consider everything.

Well, for a good worker anyhow.