Well, there are many ways to look at this. The most utilitarian is simply this: you could have a society in which people can live a decent life without having a job and without being born rich. In this society, companies could be allowed to only hire for maximal efficiency, since the state could e sure the livihood of those who don't get chosen for jobs by other means. However, such a society would be vastly different from our own - for example, it would be essentially impossible to hire for menial labor, since without the threat of starvation few people would choose to become garbage workers or maids. For another, you would necessarily have high taxes on the employed to be able to support the unemployed, which would lead to political problems and would likely be an unstable equilibrium.

In our society we have chosen a different solution, pretty much all over the world: your ability to have food and shelter is conditioned on having a job (or being born rich), but in exchange, the state tries its best to guarantee you a job. We don't generally allow the state to operate companies, so the only way for the state to guarantee jobs is to incentivize and even force companies to employ people without discrimination, to at least some extent.

Now, my personal belief is that the justification should come the other way around - why do we allow society to judge your right to a basic livelihood by any criteria at all? But I'm guessing that would not be a compelling argument, and I can't claim to have a working picture of how such a society could look like.