Potato Head was the real villain...
Sid was just a stupid kid who didn’t know what he was doing. When the toys come to life, he immediately realizes his faults. Potato Head, however, turns everyone against Woody and outright refuses to believe his innocence even when proof is present. When the toys start to accept Woody towards the end, Potato Head is the only one to maintain his animosity. He’s the reason why Woody and Buzz get into so much trouble, and their many chances to get out of the situation are ruined by Potato, who’s arrogant just because.
The later movies turned him into a likable snob, but the first movie potrays him as a flat out antagonist. He’s the villain of the first movie, not Sid.