I've been in exactly that situation, and it's definitely hard. It's infuriating to be told that you're wrong using bogus catchall arguments like "mansplaining". It's awful to be treated as the enemy when you really want to help and can genuinely contribute.
It is a useful, if aggravating, exercise to recognize that they've all been shut down many times, and this is what that feels like. Turning it around back at you is neither fair nor helpful, but it does give you a glimpse of why it's so important.
Fixing racism and sexism and other problems means working with people, and the effort won't all be focused where it should be. And saying "Well, if you won't make it easy for me then I won't help" is your privilege showing: you can walk away from it. They can't.
That's going to mean shutting up and listening, and hearing a lot that you don't like. You're not just the outsider, you're the newcomer, and they've heard whatever you have to say before. You are neither so smart, nor so insightful, nor possessed of such a novel perspective as you think. Even if they appear not to know something you know, that doesn't mean you can fix anything by saying it until you've come to a place where you understand each other's language. Because what you're listening for is a lot of stuff that you're not hearing at first, in the subtext and assumptions and connections.
So you have my sympathy, and respect for sticking with it. That's the right thing. Even if it was really awful at times.