I have 3 grown children (youngest is 16).
The second there is an adversarial feeling between parents and children, everyone has lost that part of the battle. You want kids to feel that you are all on the same side, working to help everyone learn and develop and grow older gracefully.
I think people get into trouble when they misinterpret their children's signals: fear of separation, jealousy of siblings, need for exercise, need for mental stimulation, need for autonomy, need for adventure. These are some common needs which parents often misunderstand. Bad behaviour in toddlers is often ascribed to teething, tiredness or hunger. My list is an expanded version (and applies to all children not just toddlers).
I think if you respond to what is really going on, while stopping the child from throwing things, pinching sister, etc, the need for punishments doesn't really come up.
I think the real problem with punishments is that they are usually humiliating, cause the child to lose face, and create anger (possibly accompanied by grudging compliance possibly by fiery defiance), rather than a desire to do better.
I also think that kids are very sensitive to phoniness, and that in order to do a good job of parenting without punishments you have to speak and act from the heart. Also, it is unrealistic to think that anything will always work, or will work in a smooth curve, or that you will always be loving and consistent. Honest parents admit to doing a crappy job sometimes, shouting and overreacting, but to me it was always better to stay away from coercion (rewards and punishments).