Parents are people. People deserve love, understanding, patience, and forgiveness.

People also need to be held to standards of behavior. People also need to be held accountable for not living up to those basic standards.

If your parents used to or still berate, beat, belittle, or otherwise harm you or prevent you from improving yourself, you're allowed to resent them. You're allowed to hate them as much as you would any other PERSON who doesn't live up to the basic standards of human interaction.