Describing someone as "discriminating" used to be a complement in the last century.

I'd still regard it as a compliment. I wonder if a new word will come into use for being (intransitively) discriminating? For being able to choose sensibly between options, for being able to assess whether one thing is better (for purpose) than another, for having taken the time to form an opinion on things which affect you? Or have we just lost the entire concept, the sense that it might be a good idea to know a hawk from a handsaw?

Also, "feeling discriminated against" isn't the same as being discriminated against. I'm not convinced that it's possible to legislate effectively against the possibility that someone will feel that they are being discriminated against.

extremely hard

Difficult, or ruthless?

I'm not saying that the distinction between "discriminating between" and "discriminating against" makes it easy to draw the lines between acceptable and unacceptable behaviour in every case. But I do think it's useful to remember that observing differences need not be a quality judgement.

I believe that some things are better for given purposes than others, that some things are morally better than others, that some people are better at certain things than others, and that it is sometimes possible to make not-entirely-useless predictions about how people will look/think/behave based on their demographic. It's very hard to express specifics along those lines without being seen to be "discriminating against" something.