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A three panel meme of someone riding a bike.
- First panel: Someone riding on a bike. "Reddit is imploding, quick let's get on Lemmy"
- Second panel: The bike starts to tip over on its own. "Oh shit there's too many of us, we're being defederated?"
- Third panel: They've fallen on the ground by the bike, holding their knee in pain. "Fucking Beehaw"
Not sure if I agree; sustainably can be different things for different people. For some it might be that the platform has a large number of users, but for Beehaw it is to have a safe community without bigots and trolls. It’s not sustainable for targeted individuals if they are met with hate speech, racism, transphobia etc every time they visit social media.
The Beehaw about pages explain their philosophy in more detail: https://beehaw.org/post/439918