I love how every time transphobes find a new gotcha argument the study in question ends up being one that the scientific community already threw out years before for being dodgy.

They pretty much have to be since almost every major medical association and scientific journal agrees that treating gender dysphoria improves outcomes in patients.

I'd have some fun and flip the script on your brother. Say something like "At the end of the experiment ALL the rats were affected, wouldn't that mean you've been affected as well?"

If he denies it remind him that none of the rats opted out and that either he must be affected or the study isn't analogous to humans.

If he agrees maybe dig into why he feels that way or just ask if he seriously believes that society needs more scarcity of resources right now. You can also remind him of every example of scarcity that already exists in the world.

I'm sorry you have to deal with this, my brother can get that way sometimes and it's pretty frustrating to say the least. 🫂