> because things can be put into meaningful sets.

It can be if they have meaningful attributes to differential themselves. To anchor that to social-security-paid maternity, it only relevant as an attribute if it has been considered but then rejected. Such qualification would distinguish it from any arbitrary element of the infinite set, and the qualification can be supported by facts.

> I just want to point out that there are several ways of looking at this, and several reasonable ethics.

This is why I earlier mentioned that difference feminism and Egalitarianism to be like the left and right. Both claim to have the same goal but significant different in values and ethics. Acknowledging the similarities is important, but also understand why most focus is on the differences.

> not an imaginary model of society made of spherical cows

No one has been talking about theoretical society. I could interpret it as an attempt to devalue ethics based on equality, but there we would just hit a wall of disagreement.

> try to see what conditions in real society the law is trying to address, and whether or not you think that would help.

So the law in question clump together women and children and define them as incapable to ask for support. The conditions that brought that law is ridden with cultural values of women, and caused by values that defines women as helpless victims. The local power disparity is very clear, as is the harm.

> If your goal is to minimize harm ... you just need to see which causes more harm: taking corrective action against existing discrimination or not.

Or let me put the same question. What causes more harm: Taking actions that treat people equally, or take discriminate action in order to save money.

> Victims of crimes are not a social group.

This is the second time you define what is and isn't a social group, and I don't find it fact based. To reference Robert Sapolsky, a special skill of human behavior is its ability to be part of multiple social groups at the same time. Victims of crimes is a group that deserve societys protection and understanding. Its not a place where gender should have a seven times impact. Its the other side of the coin that lets race and gender be the most significant factor in determining punishment for criminals.

> I think we have a strong disagreement over facts here.

The good thing with science is that science change when the facts change or when people provide better theories (often praised as the difference between science and religion).

> It doesn't matter how nudists consider themselves; what matters is how they are perceived by society

This is also why not all religions are treated equal. A Muslim friend once said that smaller religions that didn't have 20% global followers in the world should not have their believes respected in the same way. From egalitarianism view I disagree, and its a poor method for harm reduction.

> Whether or not naked bathing is allowed on certain beaches has no effect on the power (influence) of the nudists in society.

Since nudism is generally banned and made illegal in practically all societies except when done in excluded areas, I would say it has a very direct and explicit power effect on them as a group. We could of course say that beaches are minor thing, but so we could also say about burka wearers being denied access to beaches has no effect on the power of the Muslims in society. Just because nudists are a popular group to discriminate against doesn't make it less of a discrimination nor ethical.

Clothing is a central part of practically every culture that exist, similar to gender identity. Native culture is easiest distinguished by what they chose to wear. It is rooted deep in signaling, and can be easily identified in the most common religions to the smallest of sub cultures. Looking at nudists and transgenders, its questionable which group causes more reaction from people who defends their cultural views by denying others.

> sociologists are not concerned with feelings of rejection

Harm reduction is however important, and self identity is a key reason why society at large should be supportive of transgender rights. We should be careful when ever hate, discrimination and disempowerment is direct against people who society defines has having the wrong self-identity.

> An ethical system that would compel me to give you back your stolen car is not necessarily discriminatory towards John.

We are and have talked about equality of results. Retrieving a stolen car is more justified, and as a species we are more geared towards punishing injustice than fairness (Ref: game theory). It does however make it a poor building block for a ethical model, and a bad roadmap for equality. If cars ownership were a essential material state (and it isn't), providing cars for everyone would be an acceptable solution.

> Probably. Why? Because social activists like feminists fight for equality of power.

And here we got a key contradiction between activism done by equality feminism and difference feminism. One pulls one direction, the other in the opposite direction. Just because difference feminism believes that its for the greater good doesn't make it less of a contradiction.

A key message that this kind of gender segregation sends out is that gender-identity is a key attribute for which people should be sorted into. It creates a local power disparity, where women is viewed as worth more than men in some areas, less in other.

> What matters is whether you send a signal that some group is worth less.

This is a key aspect for most political movement, be that new feminism, Egalitarianism, mens right movement and so on. No one want to see signals that some groups they identify with are worth less all day long. Its harmful.