One of Shonen Jump's "Big Three" is Masashi Kishimoto's Naruto, and this long-running franchise is compelling for many reasons. One of these reasons is the theme of redemption and giving a second chance to those that need it, and Naruto has made many friends out of former enemies. He helped convince Zabuza to turn on his wicked employer, and other characters like Gaara, Neji and Tsunade were also won over to Naruto's side (Tsunade wasn't actually a villain, though).
In Gaara's case, he had every reason to be a chilling villain, but Naruto won him over during the battle for the Leaf Village, and Gaara became a vital ally of the Leaf Village, as well as Kazekage. In many ways, this is for the best, but in some ways, Gaara would also be a neat villain. Let's review.
10 Hero: Hope For The Sand Village
The Hidden Sand Village isn't quite as hospitable as the Leaf Village, since it's situated in a desert and has relatively few resources. Some of its recent leaders were cruel people indeed, and this is also the home of the terrifying Sasori of the Red Sand.
The Sand Village aided in Orochimaru's plan to destroy the Leaf Village, but Gaara turned his back on this effort after a point, and become a compassionate and benevolent Kazekage. That is truly what this village and its people needed after so much war and hardship.
9 Villain: Isolation And Fear
Gaara grew up with a tailed beast inside him like Naruto did, but he suffered even more for it. He didn't have an Iruka figure to help him; he was feared and hated by absolutely everyone, and this drove his loneliness and despair.
That, in turn, fueled his power and made him a highly driven and tragic young villain when he first appeared. It was fascinating, and if he remained evil, viewers could see the true depths of his despair and agony. It would sustain him as a villain for years to come.
8 Hero: Hope For Jinchuriki
A jinchuriki is the human host of a tailed beast, and there are nine of them when the story starts. These people often have it rough, and they are defined by the creature that they bear. Gaara and Naruto knew nothing but suffering as jinchuriki.
However, Naruto's stubborn optimism showed a ray of hope for these people, and since Gaara turned to the light, he repeated that lesson with great emphasis. If someone as "lost" as him could turn things around, then surely other jinchuriki and similarly cursed people could, too.
7 Villain: Formidable Foe
A good villain is a powerful one, and Gaara is indeed quite powerful. He had more control over his tailed beast than Naruto had over the Nine-Tailed Fox during the early arcs of the anime, and his powers continued to grow from there.
If Gaara remained villainous, he could pose a real threat to Naruto and his allies, especially since he gained experience from fighting them and therefore knows their fighting styles and weaknesses. That's an enemy that Squad 7 and the other Leaf ninjas would have to take very seriously.
6 Hero: Cool Rescue Mission
Gaara's capture at the hands of Deidara and Sasori is what launched the Shippuden part of the story, and since Gaara was a valued ally of the Leaf Village, Naruto and his friends (including Sakura and Kakashi) mobilized to rescue him.
Put simply, this was a thrilling and emotional part of the story, and none of it would have happened if Gaara was still a villain. He'd either be a rogue (and difficult for the Akatsuki to find), or there would be no rescue mission, since he wouldn't be a friend of Naruto's.
5 Villain: Drama
This ties into the earlier points about Gaara being a cool villain. His isolation and bitterness fueled his anger and combat power, and this leads to some personal drama along the lines of "you don't understand me" and "if I'm a monster, I might as well act like it!"
For a time, Gaara was indeed like this, and it was compelling since he was as much a victim as a villain. Some fans might say that Gaara's dramatic villain role was too short, and maybe it should have extended well into Shippuden, too.
4 Hero: Army Commander
When Gaara was turned away from his villainous ways, he not only became the Kazekage, but he also went on to lead an entire army of ninjas, too. The next great shinobi war was on the horizon, and Gaara was nominated as commander-in-chief.
This shows just how far Gaara has come, and he had what it took to lead a massive and diverse army of the world's best ninjas against Madara Uchiha and his undead hordes. No way would a villainous Gaara end up in that position.
3 Villain: More Sand Assassinations
Gaara's sand is an effective tool for defense, and the one-tailed Shukaku's power can move that sand anywhere to keep Gaara safe automatically. But this sand is also effective on offense, and Gaara wields some terrifying jutsu that uses that sand to its full extent.
Should Gaara remain a villain, he can assassinate Leaf Village ninjas with his sand, and do so in creative and unpredictable ways. Sand can go anywhere and flow into any shape, which would lead to some cool and scary assassination scenes. A heroic Gaara wouldn't do that, however.
2 Hero: Family Strength
Gaara isn't an only child; although they don't look much like him, Temari and Kankuro are his sister and brother, and once Gaara becomes a noble hero, the three of them grow closer. Temari and Kankuro become much more than merely Gaara's escorts and handlers.
Now, the three of them are a proper family, and this is a classic positive lesson of shonen manga. Family is important, as are the ties that bind people by blood or familial love. As a hero, Gaara can live up to this lesson, and create a happy family at last.
1 Villain: Shukaku Shenanigans
This is the one-tailed Shukaku, the fearsome beast that lends Gaara incredible power. This monster emerged during the battle for the Leaf Village, and wielded the power of sand and air to terrifying effect. Left unchecked, it could level entire villages.
If Gaara was a dedicated villain, then viewers could be treated to more scenes of this fascinating beast, and entire teams of Leaf ninjas would leap into battle to try and take it down, including Naruto. That would be an awesome villain for sure.