First of all, he was somewhat evil. Remember how Tigerpaw attacked Tiny (who becomes Scourge)? Well, lets think about that. Tiny would have been 2-4 moons old at the time, and Tigerpaw would be a apprentice, especially known because of the suffix '-paw' in his name. As Tigerpaw attacked Tiny, who was defenseless, and not at all hostile, and had only happened to wander into Thunderclan territory, he did nothing- in fact he rooted him on, and when Bluefur(Star) tried to get him to stop Tigerpaw, he did not. Direct quotation from the books: (Bluestar's Prophecy, page 400) “Bluefur stepped forward. ‘Now hold on, there’s no need for this –’ Thistleclaw turned on her, arching his back. ‘Shut up!’” (Bluestar's Prophecy, page 400) “The kit squealed in agony. ‘Show it your teeth, Tigerpaw,’ Thistleclaw goaded.” By doing that, he broke the warrior code. "No cat may neglect a kit in pain or danger, even if it is from a different clan." And that's terrible. Bluefur(Star) broke the warrior code too, but the code "1. Defend your Clan, even with your life. You may have friendships with cats from the other Clans, but your loyalty must remain to your Clan, as one day you may meet them in battle." Is placed for personal reasons, for the official story why it is placed is because a Windclan and a Riverclan cat were in love, eventually, in a battle between the clans, the Riverclan cat died, and the Windclan cat was caused so much pain that the code was placed. As for Thistleclaw's crime, code or not, it is unjustified.
And it is quite obvious Thistleclaw did not care about what he had done. (Bluestar's Prophecy, page 401) “’That so-called invader was a kit!’ Thistleclaw shrugged. ‘That’s his problem.’” Quite the excuse, Thistleclaw....
And why was he never chased out of Starclan? Because he was never there. Here is why.. Okay, so Vicky, one of the authors, said that Bluestar chased him out of Starclan, right? No, that is wrong. She stated it to fill a plot hole that has been correctly fixed, and she used a question mark at the end of her sentence, stating that it was a guess rather than a fact. "Unless Bluestar drove him out when she got to StarClan?!" So, it is quite obvious that it was rather a guess. From the ultimate warriors guide, we know that Tigerstar received his nine lives from Littlebird, Badgerfang, Pinestar, Whitetail, Sedgestar, Flowerstar, Redscar, Mossheart, and Cedarstar. Meaning, the plot hole was correctly filled. Thistleclaw did not give Tigerstar a life.
Also, if Thistleclaw did end up in Starclan, Bluestar is either a hypocrite or she did not chase him out. "Bluestar rested her tail on his shoulders, drawing him away from the gray warrior. “You won’t learn anything by talking to Ashfur,” she mewed. “He knows who killed him, and why. Perhaps he did a lot to bring it on himself, perhaps not. It is not StarClan’s place to judge him.” As Jayfeather opened his jaws to argue, she added more sternly, “If he found his way here, then he must deserve to be here. That is what we all have to believe.”" She directly states that if a cat were to end up in Starclan, it is meant to be and it is not worth interfering.
From this, it has become obvious she did not drive Thistleclaw out of Starclan.