Return to down (idea)

In Black English, to be down with someone is to be allied with them, faithful to them.

My homies are down [with me] so don't arouse my anger [or I will ask them to join me in expressing that anger].
(Gangsta's Paradise)

To be down with something is to accept it, either grudgingly or completely.

If you're not down with that, I got two words for you... SUCK IT.
(Degeneration X)