There's one episode of The Powerpuff Girls where they meet a new friend and when they introduce her to the professor, he says that he created the Powerpuff Girls by accident (allowing for the punchline of their friend saying she was also an accident). But the Powerpuff Girls weren't really an accident. According to the opening, he was intentionally trying to invent the perfect little girls. The only accident was putting in Chemical X, but he intended on making some girls.
And what difference would it have made if Chemical X wasn't accidentally put in? Would they just not have superpowers? Would sugar, spice, and everything nice not be enough to make a person? Would their appearances be more normal?