I don't see why people can't write feminist characters or activists in general. It'd be wrong to push a social agenda onto other players, sure, but if the setting allows it what's the problem? It's just another character. Yours even, so that's your idea. Likewise, for GM'ing, it'd be fine to boot up a roleplay about activists, the adversity they meet and their success and/or failure. I mean why not? Just don't force other people's characters to adhere by your ideals and you're all good.