Galen Marek and Cade Skywalker are 2 legends characters that fit the criteria of anti heroes that have dabbled in the darkside but they still committed acts of heroism. Galen Marek was trained as Darth Vader’s apprentice in order to execute the remaining Jedi in the galaxy. He gradually started falling in love with his pilot Juno Eclipse and he slowly grew a desire of wanting to be more than Vader’s slave. That being said he was still susceptible to the dark side during his final confrontation with Vader and Sidious.

Cade Skywalker is an ideal example of someone who deep down has good intentions but lets his darker emotions rule him more often than not. These emotions manifested themselves in an ability to heal others from the verge of death at the expense of bringing Cade even closer to the dark side.

He would use this ability whenever someone he cared about was close to death. He even though he wanted to be left alone and in peace he still did the galaxy a huge favor by waging war on Darth Krayt and his One Sith. Even though he was doing for somewhat selfish reasons, he also risked his life to protect the Jedi, his friends and even the imperial knights.

Great answer thanks.

Not to mention I love this dark side interpretation of healing as the user is unnaturally bending the flow of the force from its natural course.

The dark side is the dark side of a living thing: selfishness, fear, anger, hate, aggression, bitterness, jealousy, centered around greed. It's not malevolent, but those who are motivated by these emotions and relying on them to achieve their goals, are going to do things that are evil. On the superficial level, sometimes they won't appear as evil because it's beneficial. For example, Luke could have destroy the Death Star out of hatred, anger, out of fear of him losing his friends, out of his desire to be celebrated. The result is the same, but the amount of evil is still the same, only replaced a weapon of mass destruction with a pilot who caused mass destruction.

But it's not one thing or the other, it's a spectrum. The Jedi keep their dark side under check, so they will have it, but won't be ruled by it, and this requires diligence. The Sith are consumed by their dark side. Ventress gradually progressed from dark toward light.

Han Solo was more on the dark in New Hope, then he gradually progressed toward the light by the end of Return of the Jedi.

There was one Sith Lord, https://starwars.fandom.com/wiki/Darth_Vectivus , that used his dark side abilities for study and to aid his business pursuits instead of actually committing evil.

Interesting question. George Lucas describes the dark side in an interview as essentially being selfishness. So, I think, the more you rely on the dark side, the more you are ruled by selfish desires which, in the end, makes you less willing to help others. The needs and wants of others just don't matter to you anymore at one point. Why should you help someone if you gain nothing from it?

As WriterBuddha said, it's the motivation behind the action that matters the most, not always the deed in itself, and that's where darksiders (generally) seem to lack the aspect of a hero

I see, so the aim may be to do good but the emotion/desire to harness the dark side is a selfish desire.

In the example above where a dead master is brought to life, the aim was to save someone but it was the selfish need of not wanting someone to leave them that unleashed the power to do this.