The truth is it comes down to the exact details of the policy whether it's legal. There's tonnes of things you can do to increase diversity in legal ways. For example, Google recruits at college campuses, they must have selection criteria for which campuses they visit, no matter what that policy is it's de facto a diversity strategy.
As for whether it's fair. It seems pretty dependent on your view of the world. If your base case is that without any regulations you'll just get the best person for the job, then these programs all look like an aberration. But if your base case is that hiring isn't fair - people hire their family, their friends, people from their alma mater, people from their church etc. Then putting in a programme to mitigate the biases that do exist seems like a reasonable thing to do.
As for whether it's fair. It seems pretty dependent on your view of the world. If your base case is that without any regulations you'll just get the best person for the job, then these programs all look like an aberration. But if your base case is that hiring isn't fair - people hire their family, their friends, people from their alma mater, people from their church etc. Then putting in a programme to mitigate the biases that do exist seems like a reasonable thing to do.