"I really view this as terrorism," said James Guest, the president of Planned Parenthood of Maryland. "These are violent terrorists who are breaking the law. They've lost politically, and now they're going outside the law. It's not all anti-choice people. But there's a fringe."
For established anti-abortion groups, the violence has become a wearying problem.
Cathy Murphy, executive director of Birthright of Lancaster, said no one is sure who started the fire.
"For all we know, it could have been the angry parent of a client who's upset because their child got birth control pills. So until we know more, I don't think it does any good to point fingers."
Denise Neary, executive director of the Pennsylvania Pro-Life Federation, said the violence doesn't serve her cause.
"If anyone thinks that killing an abortionist or bombing an abortion clinic is going to protect human lives, then they're very confused and misguided," she said. "We have to restore respect for human life. To do that, we have to win minds and change hearts."
Letter condemns violence
On the night of the fire, Ms. Brogan said, someone who identified himself as a "pro-life activist," called her at home to say he disagreed with the violence. And Ms. Osgood said that an anti-abortion adoption group sent a letter condemning the act.
Tuesday, about 250 people came to a sun-dappled park two blocks from the burned clinic for a Rally Against Violence. Organizers wore "Stop The Violence" armbands.
"Violence, no matter what its rationalization or justification, is absolutely not a solution to our differences," Mayor Stork told the crowd.
Ms. Osgood took the microphone to say, "We must begin today to learn how to talk about fervently held beliefs in responsible, rational, noninflammatory ways. The rhetoric of hate, bigotry and ignorance -- the rhetoric which portrays some good and others evil -- must stop."