I'm going to tell my friends they're lazy for not donating blood
Why do you think they are lazy for that?
It's not that they're lazy, It's just they don't know how to make a good decision.
It's not realistic to expect others to always want to do what you do. Insulting your friends in this situation may not be the best route to go.
Maybe you're the one that should be criticized because you're being close minded.
I'm just saying, people don't have to donate blood if they don't have to. It's not a common thing that everyone does anyways.