nostr:npub1cmgqvz7xr07euwkum3mjghjqcu4d3k2fcyf6g4uwwe5ggnd6fetq0wrzd2 I would understand (and agree with) this if there would be context, ie. "be kind" would be a patronizing reply to someone.
Generic "be kind" is hard to find tone policing or toxic positivity in my opinion. But then again, I honestly think kindness is our superpower...