They are not specifically representing milo.
> The plaintiffs in the lawsuit are ideologically diverse: the ACLU itself, an abortion provider, People for the Ethical Treatment of Animals, and alt-right-Internet-troll-to-the-point-Twitter-actually-banned-him Milo Yiannopoulos.
It's a parade showing that the whole spectrum objects to this policy.
https://arstechnica.com/tech-policy/2017/08/dcs-transit-agen...