"The American Medical Association said 40 years ago, longer than I've been alive, that homosexuality was not a medical condition," Sims said at the Attic Youth Center in Center City. "Also in the last 40 years, we have seen a number of people claiming to be mental-health practitioners preying on parents and preying on children."
New Jersey Gov. Chris Christie signed a law last month banning the practice in his state, and a federal appeals court upheld California's first-of-its-kind ban last month.
New Jersey's law was almost immediately challenged in federal court by the Liberty Counsel, a conservative religious group.
"This bill provides a slippery slope of government infringing upon the First Amendment rights of counselors to provide, and patients to receive, counseling consistent with their religious beliefs," founder Mat Staver said in a statement released just before Christie signed the law.
Williams stressed that the Pennsylvania bill would not aim to dictate conversations in private homes and churches, focusing instead on "aggressive" therapies carried out by licensed professionals.
"This is not simply a preacher sitting down and talking about perspectives," he said.
Neither lawmaker could speak to the number of active conversion therapists in the state, noting the secretive nature of the practice.
Monique Walker, a Drexel University doctoral candidate and therapist serving black and LGBT communities, has counseled young people who have experienced conversion therapy.
"The passing of this bill is in the best interest of our young people," she said. "It sends the message that there is nothing wrong with them, nothing in need of change."
On Twitter: @jad_sleiman