Yeah, they donated their spare time to give you a decentralized platform where you could criticize them because they want to stifle "freedom of discussion"... That the lemmy.ml instance is heavily moderated on stuff like imperialist propaganda is a non-issue for freedom of expression due to the nature of federation. The devs do not even want their instance (lemmy.ml) to be the biggest, but actively promote joining other instances.
You confuse your right to express your opinions with the privilege of someone else providing you a platform for you to express them on. The devs provide the former without obligating themselves to be the ones to give you the latter.