"Nikdy není dobré nenávidět."

[chartsman]

Can I use dobře instead of dobré?

[ion1122]

No. You want the adjective "good" here, not the adverb "well".

[Samaelch]

Isn't it není "It isn't"? Wouldn't it be It isn't (ever) never good to hate

[ValaCZE]

In english you can have only one negation in a sentence.

[BelindaJua1]

"To" is not necessary in this sentence? Is it a mistake to say "Nikdy to není dodré nenávidět."?

[ion1122]

The "it" in the English sentence is a dummy place holder. Compare the following two English sentences:
1. It is never good to hate.
2. To hate is never good.

So even in English you don't need the "it"!