It's bothered me for a long time that only older people are protected against age discrimination. That restriction is unneeded for the law to be clear – it exists only to allow age discrimination against young people. Don't get me wrong, most of the age discrimination is directed at older people. But if the principle is, age discrimination is wrong and cannot be done in commercial environments as a matter of law, then you'd never add in that condition.
It's hard to explain how I view this. There's plenty in the pseudo-intellectual water supply about whether or not you can be racist to white people. But that swamp of nonsense has, at least, not been codified into law – it says that you can't discriminate on the basis of race, not, you can't mistreat black people. In no other area of American law am I aware of discrimination being legal only if you victimize a favored group.
I've had my own small trials in this regard – my own youth had little happiness in it, and some fraction of that was explicitly age discrimination. I've had a business turn me away, as a customer, while gainfully salaried and educated, explicitly because of my age. Employers as well. I've had my fair share of advantages, but if this particular disadvantage is morally wrong and unacceptable in America, as the anti-age discrimination laws seem to suggest, I don't know why it's specifically allowed in federal law.
In general, principled defenses work better when they are applied uniformly. Prohibit all racial discrimination, not just that done by white people. Prohibit gender discrimination of all sorts, and you don't need to rewrite the rules to cover sexual identity and gender dysphoric groups – you get their protections for free. It's clear you aren't rooting for one group over another – you just want to change a behavior, no matter who practices it.
Ruth Bader Ginsburg herself (before her time on the Supreme Court) argued that discrimination against men was just as bad as traditional sexism – partly due to her observation (a correct perception at the time, but dubious as a statement of absolute logical identity) that any discrimination against men represented an opposite but equal affront to women. If there is room for this stance inside whatever generation of feminism we have now (fifth?), count me in. But if you want social revenge, like those older people, discriminated against, but who wouldn't deign to share their hard-won protection with everyone... that's something I don't care much about at all.