At risk of exhibiting confirmation bias, your anecdote makes my point for me. With the ban on discrimination, your friend got misleading signals of which employers she would like, and her employer relied on weaker signals of things they can't ask about, leading to an incorrect inference -- and later, a disastrous mismatch.

So, far from eliminating the pernicious effects of bigotry, the law made people waste effort trying to route their efforts around it. Had there been no law, people could openly communicate their preferences in both directions, without having to go through the complication of sending weaker signals because they can't send the banned ones. And with less "noise", the cost of bigotted preferences becomes clearer. Explanation

I don't see why you're using this as an example of why anti-discrimination laws are good.

So what would happen if you traded the kafkaesque life for the officially-banned screening methods? Would you rather have twice the number of job opportunities and lose 3/4 of them right away because you're <insert irrelevant attribute here>? Or would you rather that other people get rejected for them, if you don't personally have many of the 'undesirable' attributes?

Certainly, you can pick the numbers to reach the conclusion that you want. But averaging over all possibilities, and weighting by likelihood, yes, I would prefer the environment that makes all job applicants not a potential albatross for employers, for the same reason I would prefer not to be exempt from lawsuits -- yes, there's a narrow benefit to laws saying "you can't discriminate against people named Silas", and to a personal exemption from lawsuits. But realistically, the way people respond to this will more than eliminate the benefit. (In case it's not clear -- do you see a hazard in associating with a stranger when you're guaranteed to have no legal recourse against what they do?)

So yes, I would rather have the option to most clearly communicate preferences, than have to dance around them, which results in situations where someone can be turned down for a job because of false beliefs that they can't even refute. This remains true, even and especially if I'm in a less fortunate end of the applicant pool (which I have been, like everyone else who has been under 14/16/18 at some point in their life).

(Btw, I'm not the one modding you down.)