Sharpay Evans did nothing wrong. While she is portrayed as the main antagonist of the HSM franchise, she did not act like many stereotypical rich blonde mean girls that are normally portrayed in the movies. Sharpay definitely has an attitude, but she never blatantly sabotages her fellow actors. She works to help Troy get into his dream college in HSM2. Despite the fact that she was crushing on Troy, she doesn't attempt to outright steal him from Gabriella. She simply requests that he sings with her at the end of the movie (which he never does). It makes perfect sense for her to be angry at Troy and Gabriella. She had gone through high school with the guarantee of getting the main role (but this did not stop her from working hard for it). Then Gabriella comes to the school, takes away the boy Sharpay has had her eyes on for years and proceeds to take EVERY part in EVERY school musical. In the first movie, the musical was everything she ever cared about, which was taken over by some random amateur people who initially weren't even interested and too scared to actually try out. They had strengths in other areas and they didn't need to necessarily be the stars in the musical. In the second movie, Sharpay just wants to relax and enjoy her summer, yet she still has to put up with the same people that ruined her entire year and took her musical away from her. Despite this, they all have jobs that she has provided and that they all need, but they find a way to complain about it the entire time. Even in the third movie, her musical is invaded once again by everyone. Yes, they have more experience in this area now than in the previous films given that this is the third movie. The point is, she never got her leading role in a high school musical, which is all she ever wanted. She was good at what she did and strived for it. The other students did not have the same ambition that she does. Everyone else decided to do the musical because it was a fun thing to do, but while doing so, they took her lead role.
Of course she is going to be outraged by all of this! How would you feel if something that you had been striving for and worked so hard to get was suddenly just taken away from you, especially if those people didn't really care whether they got it or not? Troy and Gabriella come out of nowhere with no experience whatsoever and just took over. Sharpay does not try and tear them apart; Troy and Gabriella's own friends are the ones that do that. The only thing that Sharpay Evans wanted to do was sing and perform, but everyone continually took that away from her. This does not make her the villain.
As someone coming from some theatre experience, it doesn't make any sense for Troy and Gabriella to get picked for the musical. Yes, they could sing moderately well, (even if Gabriella was nasally, and Troy was high pitched, and they were nowhere near as good as Sharpay and Ryan). Troy and Gabriella have no acting experience at all. In fact, they never even had an acting audition. I know the acting that happens while singing is just as important, if not slightly more, important to the overall production. Gabriella obviously has stage fright, and both her and Troy were super awkward. Sharpay and Ryan were a dynamic triple threat, but because they were a little mean they weren't picked. Real directors and casting people don't care if the actors are mean, they care about who can put on the best show and that was Ryan and Sharpay.
Sharpay worked hard and did not deserve to be seen as the villain. If anything, Gabriella should be seen as the true villain. Let's be real, Sharpay Evans is the best character in the High School Musical series, and if anyone tells you otherwise, they are dead wrong.