I've been thinking lately about "allies" in the social justice sense of the word: marginalised groups who have unaligned object-level interests but aligned meta-interests. Lesbians, gay men, bisexuals, transfolk and [miscellaneous gender-people] may have very different object-level interests, but a very strong common meta-interest relating to the social and legal status of sexual identities. They may also be marginalised along different axes, allowing for some sort of trade I don't have a good piece of terminology for.

As I understand social justice, that's not what they mean by ally. An ally is a privileged person who is attempting to help non-privileged people. For example, a man trying to help women (in a social justice context) or a white person trying to help people of color (likewise in a social justice context).

Social justice is an effort to put together an alliance of all non-privileged people. This can definitely get weird,

There used to be a saying that politics makes strange bedfellows-- possibly less true in the US lately, since compromise has been less attractive. Still, there can be alliances on such issues as winding down the war on drugs.